I doubt that you will find any 65mm film is used so rarely and is much more expensive than 35mm so fewer short ends if any. Also the places that sell short ends cater to the amateur and ultra low budget crowds and they can usually not afford to go 65mm. nevertheless good luckwith your search
There's a 1000' rool of 65mm 320T on eBay right now, but I'm not sure it would work in my Pentax 645's 70mm adapter. Besides, I haven't used up my Eterna 500 in 35mm yet.