where is the best way to get the missing steam cards from the sale

STM

As McMind suggested, you can use STM or just buy the cards off the community market.

You could craft another badge since that would also drop a card. For duplicates there are 1:1 trade bots in the steam forum.
But there is an easier way if you accept my friend request...

Try this bot :)

thanks sent some trade offers but - i know you can't collect any more cards after today - if i am correct - but will they still drop cards if i make sets for other cards after today as i am on a 15 day hold