I don't mess with the Axcel scopes much, but they mount the same as a Shrewd Optum, and Shrewd sells a 3/8 rod for the Hogg Father.
www.shrewdarchery.com
Looks like the SH version is currently sold out.
The lens size in the 35 and 40 optum is 1.75, same as the UV3XL, so it's an option with those scopes too. Just need to purchase the housing. LENS HOUSING
Products aren't in stock @ Shrewd, however several other vendors have them in stock.

SCOPE ROD
REPLACEMENT SCOPE ROD TO MOUNT SHREWD SCOPES ON THE SIGHT MODELS LISTED BELOW AVAILABLE IN 1/2", 3/8", AND 0.455" DIAMETER SCOPE ROD INTERNALLY THREADED FOR 10-32 BOLTS DOES NOT REQUIRE A NUT ON THE OTHER END CNC MACHINED FROM 6061 ALUMINUM SQUARE END FITS SNUGLY INTO SHREWD SCOPES TO PREVENT...

The lens size in the 35 and 40 optum is 1.75, same as the UV3XL, so it's an option with those scopes too. Just need to purchase the housing. LENS HOUSING
Products aren't in stock @ Shrewd, however several other vendors have them in stock.