So the cleanest way to fix this is to just desolder the damaged/broken switches and solder in new ones. You’ll need a few replacement (likely white Alps) switches and a soldering iron (or access to someone with a soldering iron).
Alternately, you could try disassembling the switches without desoldering and see if you can see what’s wrong with them. Usually there’s either some gunk inside the switch, or the little metal leaves have been bent out of shape, or some similar problem. If the bottom housing and switchplate are undamaged, you could even swap out broken parts for working parts from replacement switches without desoldering anything.
There are some folks on geekhack who offer repair/rework services for reasonable rates, through this subforum:
http://geekhack.org/index.php?board=160.0 – for example Dorkvader
http://geekhack.org/index.php?topic=61288.0Or if you want to go with an expert who specializes in Omnikeys, there’s always
http://www.northgate-keyboard-repair.com though I’m not sure what his rates are.