I have had one hip and two knees replaced. I've been riding my indoor Schwinn Airdyne, to keep my joints going. Now I'm ready to get back on my 30-year-old Schwinn Suburban.
My kids bought me a fancy Cannondale hybrid four years ago and I never felt comfortable on it. I probably rode it less than 50 miles. I took the Suburban to a shop for a tune-up, and they told me they couldn't get parts to fix my ten-speed gear system, so its in "uphill" mode—which is nice when I'm going uphill, but annoying when things are level.
Can a more modern set of gears be put on my old Schwinn bike, which I dearly love, and feel perfectly at home on?
—On the road again
If your doctor could find the parts to get your personal drivetrain back on the road, then doggone it—somebody ought to be able to do the same for your bike's. The short answer is yes, your Suburban can be retrofitted with a more modern system.
Shimano Tourney derailleurs and levers seem to me to be the best match in new parts that would fit your bike. The levers would be mounted right by the grips, so you wouldn't have to move your hands very far. The right-hand lever would click into place when shifting from one gear to another. The freewheel, chain, cables and cable housing also would need to be replaced. You would end up with 12 speeds instead of 10, but who's counting? It wouldn't be cheap to do—but you would likely still turn a tidy profit after selling the Cannondale. (Tell your kids it got stolen.)
However, I'm dismayed the shop couldn't come up with a part to make your existing components work. The Suburban shares most drivetrain parts in common with the retro-trendy Varsity and Continental, and lots of people in this town have experience fixing them. Have you tried the used-bike shops? City Bikes on Ankeny has a great room full of used parts for low cost.
One other thing about your bike, though: If you've ever ridden it in the rain, you know that its steel rims cause the brakes to lose nearly all their stopping power when wet. You can change to aluminum alloy rims, but that adds quite a lot to the cost. This is not an issue if you never ride in the rain, of course.