Have you tried calling the AMHR/ASPC office? They should have the official measuring stick, i think you can purchase them but they cost a bit more then the star lake/ozark measuring sticks. I think $90'ish ?
I think we bought ours from Valley Vet or Country Supply to measure ponies, I have another one that is the miniature measuring stick, both of mine has the levels built in them. If I remember correctly, they both were priced pretty reasonable, less than $50.00.
Yeap, that is where mine came from, I remember that price and its made well and does have the level. Make sure you check it out when you receive it, I had to send mine back because the level was broken when it was in transit.
Glad you found it, their prices are pretty good also on other types of supplies.