Your best bet would be to contact companies that were heavily involved with professional level racing back in the days when two strokes ruled. Companies like FMF and ProCircuit put many, many hours of R&D into their engines and have engine performance down to an exact science.
A local shop will probably not have a flow bench on hand to do preliminary flow testing, or spend the countless hours needed to evaluate the results of numerous port maps, or have the resources to waste a handful of cylinders/liners while testing is being done.
Any joe schmo with a grinder can screw up your jug, and make your powerband totally unusable.
Even if the above companies won't do the port work anymore, maybe they can recommend someone who can?
I hate to say it, but the factory designs the combustion chambers and ports for the best over all power, now polishing the ports and combustion chamber to remove rough surfaces is about all you can do, generally porting will mess up the factorys job, my 250 has a screen in the intake port, try removing it to increase the air flow, also a cam swap with more duration, with out changing the lift will change the power band, in general more duration moves the power band into a higher rev zone, which means better valve springs must be used. The big guns will use a longer connecting rod, but instead of a new piston with a higher located wrist pin, they put a spacer between the cylinder sleeve and block around five millimeters or such to match the rod length, a longer rod ratio reduces piston slap. Another simple adjustment is changing the needle hieght on the slide or changing the main jet, remember higher altitudes require a leaner mixture because the air isnt as dense, and lower altitides you can go a few steps richer, but you have to know how to read the plugs, reducing back pressure in the exhaust, will help a lot, but a jet change will help out also, dont take my advice as gospel