Same here. I called Benelli US and they assured me they are on order but said a minimum of 12 weeks. I actually did find the medium on Amazon - it was the last one at the time but keep watching and maybe you'll get lucky. But I was still too low. So I found this, also on Amazon and it makes all the difference! The cheek pad is maybe 1/8" thick and now I don't think I even need the higher combtech pad. So if you're close, maybe this will get you there. Plus the quality of the leather is way better than you'd expect for $40.
Leather Buttstock Cheek Rest with Rifle Shell Holder for .357 .308 .30-30 .30-06 .45-70 12GA 16GA 20GA .22LR https://a.co/d/bSGE9z6
Lastly, I found some companies online that will give you a Canadian shipping address and then re-mail your order to the US for a fee. Not sure how much I want to trust that but if you get desperate you could look into that.