It can be difficult to find radial tires in "vintage" sizes. This is an issue on my K75s as well. Some have solved it by mixing and matching brands to get a pair of radials on the bike. Weirdly, the cheap Shinko tires work well on it. The K75s is a 1992, but introduced in late 1980s - so I'm assuming wheel sizes are similar. (BMW is Front: 100/90-18. Rear: 130/90-17). Handling is surprisingly nimble, yet stable, on that bike - and will improve after I get the forks done right.
Hey Tim, yea the sizes on the lemans are 100-18 front 120-18 rear so not a lot of choices. It still handles surprisingly well for the vintage.