The all-knowing eBay sellers list a 1991 shift lock cable.

There's a p/n visible. Maybe helpful?

http://cgi.ebay.com/ebaymotors/Mercedes-w201-190e-Brake-Pedal-Shift-Lock-Cable-1991-/170592184471
http://cgi.ebay.com/ebaymotors/Mercedes-W201-190E-Shift-Lock-Cable-/170560064990

Another doc says it's a 190E manual and says there's a lock. And since it's on the internet, it must be true and correct!

http://www.docstoc.com/docs/71544369/w201-benz190E-manual4

I would double check any fuses that say "trans" or brake. Maybe swap the brake lights. See if theres something you can maybe jumper the brake pedal?

There's no trailer hitch by any chance? Nobody hacked the wiring for the brake wires?