Any suggestions on where to find some really nice, heavyweight split leather reins? Everything I see lately is cheap, lightweight junk. 

Have you tryed NRS? They pretty much have good quality tack or Teskeys.. 

Cowhorsesupply.com!

Rockstar Reins on Facebook makes them.   You can tell her how wide and how heavy you want them, and she can lace the ends in any color if you want.  Use code BS19 at checkout and you will get 10% off.

The Rein Man!!!! Steve does an awesome job. 

http://avleathershop.com/

The Rein Man