Hi Brad - welcome to the forum!
I would start by contacting local forklift sales/service companies in your area. That's what ultimately got Project ForkenSwift going, when a little bird told me that one company had a "forklift graveyard".
Alternatively, are there any EV groups in your neck of the woods? There are almost always components/projects for sale amongst the members.
Lastly: when you ask for a range of 50 miles and a speed of 65 mph, hopefully you don't want both at the same time.
(You'll not likely do that with lead.)