So
one of my side projects is collecting Cleveland Indians MiLB cards. Focus is on the Lake County Captains and Mahoning Valley, and then singles of specific players.
STB Sports is my go-to. I have found a random set here and there online doing specific searches, but for the most part, my only fallback is eBay. MiLB cards are weird...they can be really tough to find. I have been looking for a 1995 Watertown Indians set or the 1984 Spokane Indians Newspaper #22 Sandy Alomar Jr. card...and have yet to even see them for sale.
It's frustrating. But keep plugging along.