Hardware assistance

I've been lucky finding the right items for my windows. The channel balances are perfect, and the top sash guides I just ordered look right also. I need another critical part which I've not been able to find.
There are photos attached of this little part that fits to the end of a horizontal channel on the back of the top of the window that presses out to the frame. On both sides it serves as a cushion between the spring loaded channel and the window frame.

Thanks for your response Paul. I'll find out tomorrow if the 18-033 are right when my current order arrives. So as far as the small interlock guide is concerned, would you say that it was of the same material as the sash guide? Perhaps I can fashion something to fit in that space.