It's true that 13" tyres are harder to find, but I just bought a set of Vredestein Sprints for my Elan. Coker do all kinds!
The engines don't last as long as moderns, expect to do valve jobs etc. every 40-50,000 miles. No biggie, as you probably won't be driving the car that much but using it as a second car.
Front turrets can be repaired, but replacement chassis frame will be due at some time. That sounds a lot more frightening than it really is, especially if you are a capable mechanic. There are several excellent sources of spare parts, new and used, and a lot of helpful enthusiasts.
Take the plunge - you'll enjoy it!
'67 Elan S3
'72 Europa TC