I have a Mini30 I load for, I've never found any 'surplus' components to load, but one site had a listing for (out of stock) IMI components. the bore in mine is .310 but it does OK w/some .308 pills. I tryed some .311 125 gr (for 303 Brit) with just fair results. it does better w/.310 slugs, some of them very good. Hornady does make a .310 123 gr. slug, I bought 500 from Graf's (IIRC) and they do fine. wish there was a .310 150 gr. made but unable to locate any. my M30 seems to like 150 gr. slugs, Sierra and Speer I've used. (.308's, but POI is different than the .310 123 grs)
best results have been with Lapua catridges (123 gr.) I got off auctionarms. a little pricey and they are FMJ but wow they shoot great.
I've shot both 123 gr. .310 Win and Rem slugs I loaded with good results also. I filled a doe tag using the Win and it came apart but the big doe was dead after 3-4 leaps nonetheless.