They exist but they may be hard to find now. If you cant find one at performance-pcs you'll probably have to try AliExpress and see if you can track down a Byski or Barrow block. If that falls thru you might find a used one here in the for sale section.
You could get by with a 120 or 140 rad but if you have plans on adding a cpu to the loop a 240 or 360 would be best.
currently cooling CPU only with a closed loop 240, thats why I wanted to know what the video card would need, so custom loop with a 360 it will be most likely