Finding cubic ice CIF files in crystal database
One resource you can use is the Crystallography Open Database. Search for structures with two elements O and H, and named “ice”. You will then find several experimental structures for cubic ice:



with downloadable structure files in CIF format: 1, 2. These were done from X-ray diffraction studies and only feature heavy atoms (oxygen) positions.



Although I could not find in any open database a CIF file for cubic ice with hydrogen positions, it is easy to make one. From the paper “High-resolution neutron powder diffraction study of ice Ic”, Le Journal de Physique Colloques, 48.C1 (1987), C1-631:



you can create the CIF file yourself:

data_Ice_Ic
_audit_creation_method         'generated by CrystalMaker 9.2.7'
_publ_section_comment
;
Chemical formula (sum): H2 O

Systematic name: H2 O

Crystal structure data from: W.F. Kuhs, D.V. Bliss, J.L. Finney,  High-resolution neutron powder diffraction study of ice Ic, Journal de Physique Colloques, 1987, 48, C1-631

;
_cell_length_a                   6.358(3)
_cell_length_b                   6.358(3)
_cell_length_c                   6.358(3)
_cell_angle_alpha               90.000(0)
_cell_angle_beta                90.000(0)
_cell_angle_gamma               90.000(0)

_symmetry_space_group_name_H-M     'F 41/d -3 2/m'
_symmetry_Int_Tables_number         227
_symmetry_cell_setting             cubic
loop_
_symmetry_equiv_pos_as_xyz
'+x,+y,+z'
'+x,1/2+y,1/2+z'
'1/2+x,1/2+y,+z'
'1/2+x,+y,1/2+z'
'+z,+x,+y'
'+z,1/2+x,1/2+y'
'1/2+z,1/2+x,+y'
'1/2+z,+x,1/2+y'
'+y,+z,+x'
'+y,1/2+z,1/2+x'
'1/2+y,1/2+z,+x'
'1/2+y,+z,1/2+x'
'-x,1/4+y,1/4+z'
'-x,3/4+y,3/4+z'
'1/2-x,3/4+y,1/4+z'
'1/2-x,1/4+y,3/4+z'
'-z,1/4+x,1/4+y'
'-z,3/4+x,3/4+y'
'1/2-z,3/4+x,1/4+y'
'1/2-z,1/4+x,3/4+y'
'-y,1/4+z,1/4+x'
'-y,3/4+z,3/4+x'
'1/2-y,3/4+z,1/4+x'
'1/2-y,1/4+z,3/4+x'
'1/4+x,-y,1/4+z'
'1/4+x,1/2-y,3/4+z'
'3/4+x,1/2-y,1/4+z'
'3/4+x,-y,3/4+z'
'1/4+z,-x,1/4+y'
'1/4+z,1/2-x,3/4+y'
'3/4+z,1/2-x,1/4+y'
'3/4+z,-x,3/4+y'
'1/4+y,-z,1/4+x'
'1/4+y,1/2-z,3/4+x'
'3/4+y,1/2-z,1/4+x'
'3/4+y,-z,3/4+x'
'1/4-x,3/4-y,1/2+z'
'1/4-x,1/4-y,+z'
'3/4-x,1/4-y,1/2+z'
'3/4-x,3/4-y,+z'
'1/4-z,3/4-x,1/2+y'
'1/4-z,1/4-x,+y'
'3/4-z,1/4-x,1/2+y'
'3/4-z,3/4-x,+y'
'1/4-y,3/4-z,1/2+x'
'1/4-y,1/4-z,+x'
'3/4-y,1/4-z,1/2+x'
'3/4-y,3/4-z,+x'
'+y,+x,+z'
'+y,1/2+x,1/2+z'
'1/2+y,1/2+x,+z'
'1/2+y,+x,1/2+z'
'+x,+z,+y'
'+x,1/2+z,1/2+y'
'1/2+x,1/2+z,+y'
'1/2+x,+z,1/2+y'
'+z,+y,+x'
'+z,1/2+y,1/2+x'
'1/2+z,1/2+y,+x'
'1/2+z,+y,1/2+x'
'1/4+y,-x,1/4+z'
'1/4+y,1/2-x,3/4+z'
'3/4+y,1/2-x,1/4+z'
'3/4+y,-x,3/4+z'
'1/4+x,-z,1/4+y'
'1/4+x,1/2-z,3/4+y'
'3/4+x,1/2-z,1/4+y'
'3/4+x,-z,3/4+y'
'1/4+z,-y,1/4+x'
'1/4+z,1/2-y,3/4+x'
'3/4+z,1/2-y,1/4+x'
'3/4+z,-y,3/4+x'
'-y,1/4+x,1/4+z'
'-y,3/4+x,3/4+z'
'1/2-y,3/4+x,1/4+z'
'1/2-y,1/4+x,3/4+z'
'-x,1/4+z,1/4+y'
'-x,3/4+z,3/4+y'
'1/2-x,3/4+z,1/4+y'
'1/2-x,1/4+z,3/4+y'
'-z,1/4+y,1/4+x'
'-z,3/4+y,3/4+x'
'1/2-z,3/4+y,1/4+x'
'1/2-z,1/4+y,3/4+x'
'3/4-y,1/4-x,1/2+z'
'3/4-y,3/4-x,+z'
'1/4-y,3/4-x,1/2+z'
'1/4-y,1/4-x,+z'
'3/4-x,1/4-z,1/2+y'
'3/4-x,3/4-z,+y'
'1/4-x,3/4-z,1/2+y'
'1/4-x,1/4-z,+y'
'3/4-z,1/4-y,1/2+x'
'3/4-z,3/4-y,+x'
'1/4-z,3/4-y,1/2+x'
'1/4-z,1/4-y,+x'
'-x,-y,-z'
'-x,1/2-y,1/2-z'
'1/2-x,1/2-y,-z'
'1/2-x,-y,1/2-z'
'-z,-x,-y'
'-z,1/2-x,1/2-y'
'1/2-z,1/2-x,-y'
'1/2-z,-x,1/2-y'
'-y,-z,-x'
'-y,1/2-z,1/2-x'
'1/2-y,1/2-z,-x'
'1/2-y,-z,1/2-x'
'+x,3/4-y,3/4-z'
'+x,1/4-y,1/4-z'
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'1/2+x,3/4-y,1/4-z'
'+z,3/4-x,3/4-y'
'+z,1/4-x,1/4-y'
'1/2+z,1/4-x,3/4-y'
'1/2+z,3/4-x,1/4-y'
'+y,3/4-z,3/4-x'
'+y,1/4-z,1/4-x'
'1/2+y,1/4-z,3/4-x'
'1/2+y,3/4-z,1/4-x'
'3/4-x,+y,3/4-z'
'3/4-x,1/2+y,1/4-z'
'1/4-x,1/2+y,3/4-z'
'1/4-x,+y,1/4-z'
'3/4-z,+x,3/4-y'
'3/4-z,1/2+x,1/4-y'
'1/4-z,1/2+x,3/4-y'
'1/4-z,+x,1/4-y'
'3/4-y,+z,3/4-x'
'3/4-y,1/2+z,1/4-x'
'1/4-y,1/2+z,3/4-x'
'1/4-y,+z,1/4-x'
'3/4+x,1/4+y,1/2-z'
'3/4+x,3/4+y,-z'
'1/4+x,3/4+y,1/2-z'
'1/4+x,1/4+y,-z'
'3/4+z,1/4+x,1/2-y'
'3/4+z,3/4+x,-y'
'1/4+z,3/4+x,1/2-y'
'1/4+z,1/4+x,-y'
'3/4+y,1/4+z,1/2-x'
'3/4+y,3/4+z,-x'
'1/4+y,3/4+z,1/2-x'
'1/4+y,1/4+z,-x'
'-y,-x,-z'
'-y,1/2-x,1/2-z'
'1/2-y,1/2-x,-z'
'1/2-y,-x,1/2-z'
'-x,-z,-y'
'-x,1/2-z,1/2-y'
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'1/2-x,-z,1/2-y'
'-z,-y,-x'
'-z,1/2-y,1/2-x'
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'3/4-y,+x,3/4-z'
'3/4-y,1/2+x,1/4-z'
'1/4-y,1/2+x,3/4-z'
'1/4-y,+x,1/4-z'
'3/4-x,+z,3/4-y'
'3/4-x,1/2+z,1/4-y'
'1/4-x,1/2+z,3/4-y'
'1/4-x,+z,1/4-y'
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'3/4-z,1/2+y,1/4-x'
'1/4-z,1/2+y,3/4-x'
'1/4-z,+y,1/4-x'
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'1/2+y,3/4-x,1/4-z'
'+x,3/4-z,3/4-y'
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'1/2+x,1/4-z,3/4-y'
'1/2+x,3/4-z,1/4-y'
'+z,3/4-y,3/4-x'
'+z,1/4-y,1/4-x'
'1/2+z,1/4-y,3/4-x'
'1/2+z,3/4-y,1/4-x'
'1/4+y,3/4+x,1/2-z'
'1/4+y,1/4+x,-z'
'3/4+y,1/4+x,1/2-z'
'3/4+y,3/4+x,-z'
'1/4+x,3/4+z,1/2-y'
'1/4+x,1/4+z,-y'
'3/4+x,1/4+z,1/2-y'
'3/4+x,3/4+z,-y'
'1/4+z,3/4+y,1/2-x'
'1/4+z,1/4+y,-x'
'3/4+z,1/4+y,1/2-x'
'3/4+z,3/4+y,-x'

loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_occupancy
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
    H1    H  0.5000      0.4670(19) 0.4670(19)  0.4670(19)
    O1    O  1.0000      0.3750     0.3750      0.3750