AFAIK there are no standard sizes. I've just today collected several panos from the printer. 460 x 1500 mm, 300 x 900 mm, 400 x 1200 mm.... They will be mounted on Dibond or Alubond foam, the customer can have them framed somewhere at the supplier of his choice. Custom made frames are just a fraction more expensive than standard frames. BTW, what is a 'standard frame'?
In the US frames come in 5x7, 8x10, 11x14, 16x20 etc as standard sizes.