Having a harder time finding Panini rookies on eBay

I’ve been aggressively collecting UFC Panini rookies for almost a year now, and as time as gone on I find it harder and harder to grow the collection. It seems like there are fewer cards being listed on eBay that fit my interests, and when they are listed the prices are well outside the range of what I’m used to paying. Is this an eBay thing? Are there other marketplaces that are becoming more popular? It used to be that I was tempted multiple times in a day by an auction that was ending or a new card that just went up. Now maybe once or twice a week I see something juicy and I’m making purchases I wouldn’t make otherwise just because I’m jonesing.