You'll want to check junkyard listings on car-part.com or skim places like Craigslist or FB marketplace to see what's around. Not sure what rebuild parts are on the market, since it's not a common engine that gets overhauled. I'm sure some manufacturers make the parts, but if you're just looking to get up and running, a used engine will probably do it for a fraction of the cost.
Good luck, I know Series 1's aren't the most discussed or tinkered with, aside from a rare few who went that route.