Since Horizon is the exclusive US importer, and everyone else gets it from them, it's going to be tough.

I was at Roy's Hobby Shop in Hurst TX last week and they had a pretty good selection

They have a website www.royshobby.com but it pretty much says 'give us a call'
The 'online store' link is just a portal to Horizon so it is worthless to you since you already know they're out of stock.

(817) 268-0210
Monday through Friday 11 am until 7 pm central time
Saturday 10 am until 6 pm
They're closed on Sunday and I have no idea if they do mail order.

A phone call is cheap enough to find out if they can help you.