Suzuki 2 Strokes

Is it is still possible to buy pistons for a 1976 European spec GT550 with the Nikosil bores from Suzuki?

I think you will struggle to get Suzuki standard bore genuine pistons. Oversize are available from various sources but thats for the iron liners. You can buy cruising image replacements
https://www.ebay.co.uk/itm/72-77-SUZUKI ... 3d3e1c474e" onclick="window.open(this.href);return false;
There are good reports on the quality.
Then there are Wiseco pistons a bit more expensive!
https://www.ebay.ie/itm/Suzuki-GT550-no ... Sw44BYM52t" onclick="window.open(this.href);return false;

I suppose that I would be too optimistic to think that just a barrel and piston change with a iron liner one might get me going again?

I wouldn't run an engine with one different barrel. It's all three the same IMHO. The SCEM or Nikasil have additional ports too.
The idea of the SCEM is to make the piston rings only as the wear item whereas the iron bores and rings can wear out.

GTandcbr,

I wasn't thinking of just one barrel, you'd have to do all three!

Yes agreed. Then no problem personally i prefer iron bore as the SCEM is expensive to repair. But thats just my opinion

The iron barrels will fit but are not a perfect match for the transfer in the case.