I have a Dacor 950XL set myself and love it. If your 950 has the single spring configuration then the standard HP seat from Trident will suit perfectly. If your 950 has the earlier double spring arrangement then get eBay item number 160847711238 and give it to you technician and you should not have a problem. I cant remember if this kit includes the HP seat itself or not but as already said you can order one from Trident. I suggest once you get it overhauled this time and know exactly what parts you need then get yourself 2 sets of parts for it, keep one in your reg bag for emergencies while travelling and the second you can use to provide a reference for ordering replacement parts in the future. I also recommend you try and find yourself a technician that is a Dacor fan they are out there but can be hard to find. The biggest issue with Dacor gear I have found is finding the right guy to work on it once you find him stick to him and you will know that he will always have the parts in stock for your gear.
I would also recommend looking into getting another set of regs to use as backup or standby. Something where parts are not a problem.
They don't need to be expensive or brand new... I would recommend a Mares Abyss/Voltrex - MR12 combination as you will find it breathes in a similar way to your 950 set, although it is different mechanically, it is extremely reliable and parts are unlikely to ever be a problem. You could also look at Subapro gear second hand it's quite affordable and it's one of the market leaders for a reason.