When a new collection is released, it is only available for a limited amount of time before it "retires." Collections are only considered "active" for around 1-3 months before they are retired (certain special collections are sometimes only active for a week before retiring).
Once a collection retires, the cards are no longer found in the active markets; they are instead relegated to retired markets. Cards in retired markets all require tickets, so if you do not want to use tickets to complete the collection, you will need to steal/trade for these cards, or hope to find some in the Fort Worth/Moscow auction market.
To see when a collection will retire, go to your Vault and click 'Active Collections' on the drop down bar. Then, click whatever collection you want to see when it will retire; for example, the First In Space collection will retire on June 17, 2016: