If you ever have the time or inclination... the FDR library in Hyde Park, NY is a great resource for images of FDR, most of which are now in the public domain, and easy to obtain copy prints from. I've done photo research there, and it's a lot of fun to go through their files. Anyone interested in the history of FDR's presidency would be well served by a visit there. You may need a "reason" to get access to the files... I was working for a well known news magazine at the time, but I think just about any freelance researcher can get access, provided you give some indication of their purpose.
In other words, they can't be licensed for commercial purposes, but I think any history buff can acquire prints. Seeing original negatives... that's a different story, and I'd bet a lot of the negatives from that time are pretty delicate.
One interesting note... only two photographs exist of FDR shown in his wheelchair. One can be found on his Wiki page, and there is another where he is talking with a group of people, and you only see him from the back, IIRC.
His wiki page has one of those wheelchair pix, though cropped to a square from a vertical with a bit more breathing room.
http://en.wikipedia.org/wiki/Top_Cottage
All that said, I would be very suspicious of anyone offering "original negs" of FDR since the copy prints are so easily obtained.