Think this was discussed before, but could not find the thread

Are there collectors who look for a certain number of a card (ex 5/5, 5/10, 5/25, ...) and if so what is the best way you find these. Is there a place to list what number card you are looking for and see if anybody has it and is willing to trade a similar card for it.

I recently picked up a few Ralph Macchio 2009 Americana Cards and there are different parallels (Gold x/50, Gold x/100, Silver x/100, Silver x/250). Since the card is Number 21, would be interested in trading the ones I have for for the 21/xx cards. Also would trade for the 28/xx card as that is my favorite number and it would be cool to have all of the 28/xx cards

I have known a few people who have worked on numbered sets. It has been a multiyear challenge and it was usually a set they were in love with.

As far as going after certain numbered cards, I have nothing to offer there.