Where can I find ranges of isotope abundances?
I am aware of this range diagram about $\ce{^{81}Br}$ that appeared in the recurrent (open access) IUPAC recommendations of atomic weights in Pure and Applied Chemistry:



(source: doi 10.1351/PAC-REP-13-03-02)

which cites data of a publication in Environmental Chemistry extending a little to $\ce{^{37}Cl}$ (doi 10.1071/EN10090, open access), too.  

Even if the elder (2000) IUPAC compilation in the same journal includes a graphical representation of the range in occurrence of $\ce{^2H}$ as known at this time:



(source: doi 10.1351/pac200375060683, open access)

it may be worth to read more in detail, as -- in contrast to the 2011 edition (32 pages) -- the 2000 edition (120 pages) includes a dedicated section "Isotope fractionation from natural processes" and "Element-by-element review of the standard atomic weights" for a detailed view.



Otherwise, if you were "just" interested in an overall overview of isotopes, their masses and their percentage of occurrence, NIST has a searchable dedicated database here.