I think the 87-89 KX250 pipes will work, but just want positive confirmation from someone.
You could use a 86 Tecate pipe but you would have to cut the stinger and mount a FMF universal Turbine Core 2 silencer.
DG still sells the Tecate pipe new.
I still have a 1986 KX250 PC pipe and it is for sale
here is a PC 1986 KX250 pipe on my Tecate: