I think that it will very difficult to generate carbenes from alkenes or isocyanates likewise I believe that you will not find references. Concerning epoxides, its known that you my try JACS, 2004, 126, 8664; J. Org. Chem. 1976, 41, 1421; Lithium amide bases seems to work in some cases. Hope may help.

Carbene from simple alkene is not possible. How ever the synthesis of alkyne from dibromo alkyne goes through carbene intermediates. (corey fuch reaction).

If there is no hydrogen in the olefin you can try to trap the carbene

Sterically hindered alkenes can give carbenes by thermolyses. eg. tetra-1-nathphylethylene. Aryl substituted Oxiranes will give aryl carbenes by photolysis.

There are numerous review articles accessible through scifinder.