A lot of the TSP sold now in the US is actually Phosphate free TSP. As crazy as that sounds (Tri Sodium Phosphate without the Phosphate is what exactly?), the product that is typically sold in its place is 100% Sodium Metasilicate which is also a strong base. Additionally Sodium Metasilicate is the active ingredient in PBW. PBW is composed basically composed of a strong base and surfactants.
Bottom line 2 Parts sodium metasilicate(TSP from ace) to 1 parts Oxyclean (or some other washing sodea) will work great and is a fine replacement for PBW.
For a further discussion check out the PBW vs OxyClean debate.