Good Morning, I live just north of you a couple of hours. I do have an old Howard thinking 72 inches, It is sitting out n the yard, In it's day it was a fabulous machine we broke a lot of prairie with it and eventually it just more or less got set to the side. I replaced the drive chain on it but the bottom seal leaks terribly, it is a different pitch chain than the original, So yes, parts are VERY hard to come by. I have since replaced it with a newer model Sovema, not a Howard it is 82 inches and it seems to do a great job, We used to run the Howard on a 4020 John Deere and breaking prairie it would make that 4020 snort at times.
Regarding going with a newer model I would definitely go for it. Sure it isn't a Howard, but parts availability , and dealer service do count in My books. The Howard however is definitely the Cadillac of tillers. For an implement that would perhaps get 30-40 hrs a year it would take a long time to wear out a new one and at least you know what you have going in at the start.
But if you do decide to go with the Howard, come on up and grab this one for parts, I'll load it up for you!!
Cheers
Roger