Wherefrom I can buy yellow ones for Firebird -91?
Original is red but I need same colour like front ones.
Any suggestions?

 

Check your state laws, before you go spending $ on things like that.

My state requires amber front, red rear, for identifying which way a car is facing from a side view.

Yellow/amber on the rear sides may not be legal & get you not only tickets, but cause the car not to pass Inspection.

 

I just realized your from Finland so there may be no issue with your colors being changed.

With that being said...

The 'bird ambers & red lenses are the same size, so just get you some amber lenses & put them in place of the red ones. Simple swap!

 

Yes, I`m from Finland and ours law says that only legal colour is amber.
Every year I have to fight with this, but now I don`t have the energy any moore.
But as I remember that they are different size, front ones is wider than rear ones

 

I just looked at my spare lenses & your right. The red rears are about 1" longer & about 1/8" taller, than the amber fronts.

So I guess you'd hafta either make amber lenses for the rears or swap in clear lenses & put in amber bulbs.