I heard that in order to lease a seat, your FCM must guarantee the seat value to the lessor. IBKR wants a really large equity cushion to do this even though the seats I'm looking at are around 40k to 200k.
How about calling directly the lessors ?
The list (contact persons and phone numbers) can be found from this page:
https://www.cmegroup.com/company/membership/membership-and-lease-pricing.html