Try Volvo 240/245 handbrake assembly, fits flat to the top of the tunnel so it can be mounted anywhere and by using a couple of off the shelf lengths of steel M8 tubing you can run the original cables over the top of the chassis.
I fitted my gear change (Skoda 1300) first and it just happened to be in over the handbrake position and then I worried about a handbrake and I too looked at various types including umberella handle, side mounted, hydraulic, (illegal then) etc and after driving my local scapyard nuts came up with the Volvo one for £5, has a bandbrake warning switch built in as well and is fully adjustable. cables just need a bit triming off of the threaded part.
Peter