Sorry, RadarMan, I can't find .351 in any current ammo list. The .351 was an upgraded .35 Winchester.
The guns were pretty popular gun with LE, prison guards, and the like, but became obsolete years ago. Some guns were sold to the public. During the riots in DC in '72, I remember seeing, at one Government agency, a GSA guard with an armload of Model 07s handing them out to the other guards. I wanted to try to buy them, but didn't think that was the time to make an offer. I have no idea what happened to them - probably scrapped.
For ammo, best bet is Old Western Scrounger or old hardware and sporting good stores. Maybe it can be made out of something else. I'll check Nonte's book and let you know.
It is a straight case and should be fairly easy to reload, but would have to be kept within narrow limits due to the straight blowback action of that gun.