Leland's has an auction going on until June 30 with a bunch of sports items. Starting with Lot 143...
http://lelands.com/Lots/Gallery
1972 mounted shoe from Secretariat's maiden win
1972 set of 8 nails from one of Secretariat's shoes worn in the Belmont Futurity
1978 mounted shoe from Slew's Woodward
2006 mounted shoe from Barbaro's Preakness
1975 shoe from Ruffian's Acorn
2014 shoe from American Pharoah (I guess from sales prep, it says from a groom at Taylor Made)
...plus a halter from Pharoah, a 1940s saddle, Seabiscuit program collection, and some other stuff