Alfa Aesar sells the superoxide (KO2).  I believe you could make K2O by reacting this with K metal if you needed it to be K2O exactly.  Hope this helps

I found this - KO2 + 3K = 2 K2O (700° С, p) - I think the p means pressure though - wasn't specified

Also you could do - 2 KNO3 + 10 K → 6 K2O + N2

But K2O sounds pretty air sensitive and this reaction is going to produce some gas (so a sealed vessel may be a poor choice to keep it dry)

After heating the KOH , I think you will get K2O

KCl also  

Hi ,

You may make inquiry at Alfa Chemistry, they offer kinds of chemical for research use.

https://www.alfa-chemistry.com/order.htm

Potassium monoxide can be prepared in laboratory by reaction of potassium nitrate with (excess) liquid potassium at 170 ºC: 2 KNO3 + 10 K → 6 K2O + N2.

Cf.: M.G. Barker, A.P. Dawson, "The reactions of the oxides Cu2O and CuO with potassium monoxide and liquid potassium", J. Less Common Metals, 64(1), March 1979, 127-134.