Long live the .41mag! Perfect for every occasion.
That reminds me, a neighbor gave me an old tool bag, loaded down to busting with various brass, bullet heads and even a few ancient loaded rounds of "thurty-thurty". But MOSTLY .41 mag brass and heads. Since I don't HAVE a .41 mag anything, I'll want to trade those off for something...
As far as "old timey" "obsolete" cartridges go, HA! Try to find a decent supply of .375 Winchester! I bought a mint Marlin in that caliber, intending on making it a fine black bear rifle, until I couldn't find any ammo for it at all. (Okay, the tiny amount I DID find was so outrageous, it was hopeless!) That was, of course, until JUST after I sold the rifle for a 45-70, THEN I couldn't go through a gun show without tripping over some... (my luck!) It would have stayed like that had I kept that .375 for 20 more years, too!
My cartridge that I love that everybody calls "obsolete" is that darn .357 Sig, I LOVE that round in both my G32C and a KKM barrel converted G35, best compensated gun I've every used for the 32C and crazy accurate in both. Luckily, I bought a bunch of .357 Sig from TSUSA years ago.