Couple things.....
1. Welcome to the site. Lots of good people and lots of good information here.
2. I have an outfit on a Triumph but it's a late model Bonnie, not an R3
3. I'm the Michigan State Rep for the USCA, the same folks that sponsor Sidecar.com
4. Aremec's are superbly built chairs, however they are pricey.
5. There are a number of manufacturers in Europe and here in the states.
6. The problem with an R3 is that the engine is a stressed member, that is, a part of the frame. Consequently, because of the forces the chair (sidecar) exert on the tug (motorcycle), especially during cornering and with a passenger/cargo in the chair, a sub frame has to be constructed and added to the R3 to properly carry the sidecar attachment points in a triangulated manner.
7. I would strongly suggest obtaining Dr. Hal Kendall's book or CD on sidecaring and proper setup, before embarking on what will be an expensive journey that, in the end, you might not be at all comfortable with or want to ride.
Sidecars drastically change all the handling attributes of a 2 wheeled motorcycle and not for the good except in one instance and that only instance is stability on less than ideal surfaces like gravel, dirt or wet/snow covered roads.
Another thing to keep in mind is that a sidecar is work to ride because, with no sidecar, you lean and counter steer the motorcycle to negotiate curves. Crowned roads automatically induce the required counter steer to maintain a vertical riding position, none of that works with a chair because of the geometry. You don't counter steer most outfits with the exception of the Equalean and I believe some Aremecs because of the sophisticated (and very expensive frame) that allows the chair to 'lean' with the tug.
Most bikes manufactured today don't have enough trail built into the forks (because less trail makes for easier 2 wheel steering)(but unstable offset 3 wheel steering with a chair attached). Consequently, many owners change the front telescopic forks to an Earls style, leading link front fork to get the proper trail and rigidity because the front forks take a tremendous amount of side thrust with a chair attached.
8. While sidecar equipped bikes look 'neat', they don't ride or handle like a normal motorcycle, ion lots of ways are a pain in the arse to ride and deal with and you have to develop a whole new aspect to riding which is probably why there aren't too many outfits out there and used ones are hard to sell.
That brings me to a pint and that is, I'd suggest getting a ready made unit such as a Ural or a Chinese Chang-Yang and riding that before spending what will be considerably more than the price of either on a top flight outfit. That way, you can see if you are indeed comfortable with an offset 3 wheeler and not forever alter the R3 that you already ride.
Good luck.
