Other than general repair like bearings ; I don't think there is anywhere that extra parts could be obtained as you suggested. I know that Turbine Solutions
is planning to keep the Wren 44 TP in production ( now called the 45i) except the anodized color of the case . Not sure of any internal changes as the power hot end
is the same for regular turbine as is the Turboprop. The only thing is, if sent to them they would know of any upgrades to internals plus you can get an
upgrade to an Xicoy ECU and newer pump or whatever.