You did fairly well. Carcanos don't sell particularly high because they have a largely undeserved bad reputation from a long history of misunderstandings. The M91 is one of the least commonly encountered Carcanos (the M91 Cavalry Carbine and M38 Short Rifle are much more common it seems). Your rifle should be chambered for 6.5x52 Carcano and will be old enough to have gain-twist rifling (the twist rate in the barrel gets progressively faster from the breech to the muzzle).
In order for the rifle to work as designed, you will need not only ammunition but also clips. Carcanos use 6-round Mannlicher-style clips which are made of either steel (black finish) or brass (gold finish). The entire package consisting of the clip and six rounds of ammo is inserted into the magazine and the clip stays in the gun until the last round is chambered at which point it falls out the hole in the bottom of the magazine. Italian military ammo originally came already packed onto the clips similar to the way 30-06 ammo was issued already packed in 8-round en bloc clips for the Garand during WWII and Korea. You can sometimes find surplus ammo still on clips or the clips can be purchased separately ($5-10 a piece seems to be the going price on Carcano clips). I would only buy surplus ammo for the clips as surplus ammo in this caliber is absolute crap (extremely corrosive and very prone to misfires and hangfires). Also, guns in 7.35 Carcano use the same clips, so if you find ammo of that caliber on clips for a good price it may be worth your time and money to buy it.
As far as ammo is concerned, forget about surplus because, as I mentioned before, it is a waste of money, time, and frustration. Currently, four manufacturers make 6.5 Carcano ammunition: Norma, Hornady, Prvi Partizan, and FNM. Of the four, Hornady is the best because they are the only ones to use proper weight and diameter bullets. You see, unlike most other 6.5mm cartridges like 6.5x55 Swede, 6.5x50 Arisaka, or 6.5x54 Mannlicher-Shrouner, 6.5 Carcano uses a .268" diameter bullet rather than the more common .264" diameter one. The standard bullet weight for 6.5 Carcano is also an unusually heavy-for-caliber 162grn (most 6.5mm cartridges use a 140grn or lighter bullet). Most of the reputation for inaccuracy that the Carcano has gotten comes from the use of undersize .264" bullets. Using bullets of that diameter in a Carcano usually give accuracy ranging from mediocre to something resembling a shotgun pattern.
Hornady loads a 160grn RNSP with a .268 diameter bullet for this cartridge while Norma, Prvi Partizan, and FNM all use 123-156grn .264" bullets of either FMJ or JSP type. FNM and Prvi Partizan ammo are, however, usually significantly less expensive than Hornady or Norma and are good sources of boxer-primed brass if you intend to reload.