buck-boost, SEPIC IC out 3.3V and min 500mA 0.1" packaging
As OP has not clarified what 6V depletable source is to be used, this answer predicates a battery which has a nominal full charge voltage of 6 Volts, and is operable down to 3 Volts. 

As discussed in comments, there are few if any options for an integrated buck-boost device in a 0.1 inch pin pitch DIP form factor. Further, with most manufacturers DIP is rapidly going out of production to be replaced by SMD, so it is inadvisable to use a DIP part for a new design, even if one finds such an option.

A parametric search for SEPIC / buck-boost ICs with the stated criteria, on a major vendor site such as DigiKey yields several options in SOIC packages. These are leaded packages with a 0.05 inch pin pitch, not extremely difficult to hand-solder. One DDPAK-5 

Examples:


Linear Technology LT1572:

1.25 Ampere monolithic switching regulator with inbuilt switching MOSFETs, in SOIC-16. Operates from 3 Volts to 30 Volts. Supports most switching topologies including SEPIC.
On Semiconductor CS5171:

1.5 Ampere switching regulator with inbuilt switching MOSFETs, in SOIC-8. Operates from 2.7 Volts to 30 Volts. Similar to above, supports several topologies including SEPIC.