Yes, the hobby shop. THE HOBBY SHOP sold you a defective kit. THE HOBBY SHOP is ultimately responsible.

THE HOBBY SHOP asked RT for a new canopy so they could give it to YOU. YOU did not get one from THE HOBBY SHOP.

THE HOBBY SHOP still owes you a good canopy for the plane you bought from THEM.

If THE HOBBY SHOP cannot get one from RT, then THE HOBBY SHOP needs to make it up to you somehow and if THE HOBBY SHOP cannot get satisfaction from their supplier, they should stop doing business with them.