Quote:

"Aaaahh ! So, it's a question of availability..........."

Not available because they aren't practical. You don't see two stroke gassers powering certfied 8 place full size planes either !

A small 4 stroke gasser would sacrifice :

1) Power, Methanol fueled engines have higher output than gassers.

2) Cool running , Gasoline burns hotter.

3) Weight, The addition of a spark ignition system would add considerable weight and take up space not always plentiful in smaller planes.

The big gassers fly great. We have the engines for them because they are practical.
Sport flyers have a broad range of fine four strokes to choose from. We are very lucky ,they came just in time to save many fields we may well have lost due to the objectionable sound of the two strokes.
Are they worth it ? the percentage of four stroke flyers is growing constantly. Many people now fly four stroke ONLY !

More power to 'em