I have one that's pristine. I'll sell it for $450 or $600 with the pump (it's a year old and has the QD adapter to match the rifle). Don't pay more than that on the trade, because mine's NICE.
You need a .457 bullet, you can get them here:
45 slims
EPP-UG 36.00/250 155 grain sized to .454
45Slim 26.00/250 165 grain sized to .452-.454
Those two shoot really well in mine, but if you ask for the "as cast" you might be better off.
If you want to shoot round ball, Midway carries .457 blackpowder balls, the Speer seem to be higher quality.
If you look in the "Hunter of the Year" thread, that's the same rifle as my hunting partner used to kill the coyote. My rifle's a lot newer than his, but he has had a tuning job and it turns a little better velocity.
PM me if you want any questions answered. I haven't shot mine a bunch, but we've got a lot of accuracy and chrony data on the 909.
"How do you put the air in them?? "
Pump it in with the Hill pump to 2900 psi, then you're good for about 6 full-power shots until the velocity starts to drop off.