I'd get your request to reserve a rental fairly soon, if the dealers have a big backlog of orders. There are likely not a ton of people buying high ticket items right now, but the supply is limited.
Personally, this is a lens I'd probably rent, along with a appropriate head.
Canon USA gets them in batches, so if you call a dealer, there is a possibility that they will have some idea. Everyone will get a allocation when the next batch arrives, and pre-orders may take all of them, or there may be some left over. You can' of course, get one on ebay from Japan, but getting it serviced might be a hassle, and, if it is damaged in shipping, it will be extremely frustrating.
I've had good luck getting hard to find lenses from Adorama, and poor luck with Amazon and B&H.
Call, don't email your favorite dealer and see what they say. Its possible that they get shipments every two weeks and can have one for you soon.
I see that Patriot posted while I was writing (slowly), Call Adorama, they may get a couple of extras.