There have been a few previous threads on this but RVUpgrades.com, a forum sponsor and whose owner is the founder of iRV2 forums, is a seller who I believe will honor the Blue Ox trade-in program (Blue Ox is also a forum sponsor). RVupgrades will have competitive prices and usually will beat competitors on most items with some of the best customer service around. I'm not sure how the trade-in transaction works but you can call them to find out.
This mentions the trade in program but the link on that page to the trade in program appears to be gone:
RVupgrades.com - How to Tell When You Need To Update Your Blue Ox Tow Bar
Here's one of those previous threads that discuss the good prices for towbars at RVupgrades.com:
Blue Ox Trade-In?