Any competent gunsmith can rechamber the rifle. Chamber reamers can be easily rented. For your rifle, the rechambering merely involves slightly lengthening the chamber.
Actually, if you are somewhat mechanically inclined, you could rent a reamer and rechamber the rifle yourself. It is that easy.
However, before rechambering, if you are looking for a round that you can buy in a store, then your suggestion of reboring to 30/30 makes more sense. I suggest you call Norman Johnson (High Plains Re-boring & Re-rifling) at 701.448.9188.
Other calibers that you could have your rifle rebored to are the 25/35 and the 38/55. Ammo wouldn't be on Walmart's shelf but can be found via the internet.
The 25/35 is listed as a 6.5x52r. (It was adopted by numerous Continental rifle makers). It is a fairly mild cartridge and fun to shoot.
