Hey, Im new here, I have a Das Keyboard with custom keycaps. I have a few questions.... Where are keycaps sold on this website, I realize there is a marketplace but its not really clear... Also, can you guys share your opinion on my keyboard and the design please?

DT is not a vendor, just a forum. Members often have stuff to trade or sell, but if you want to buy ready made caps your best bet is WASD, SP, or qtan...WASD and qtan are easy to contact via geekhack.

Finn, maybe you're looking for the Doubleshot Replacements Round 4 thread:
viewtopic.php?f=11&t=1376
Make sure to read and understand ( ) the wiki:
wiki/Doubleshot_Replacements_Round_4