Substitutions for vegetable oil in cornbread

I generally clear my clogged misters / spray nozzles by unscrewing the spray part from the bottle and then submerging the uptake tube in very hot (but certainly not boiling!) water and then pumping as long as it takes to clear the clog out and start spraying a mist / spray pattern again. The hot water should be enough to break up the clogs, and the pump action should force the clog out.

The "solid vegetable oil" you're describing sounds like Crisco (shortening), which you can find in any US grocery. You could also try refined coconut or palm kernel oil, both of which are solid at room temperature.

Another possibility to note is that the butter may be fine, but maybe the chickpea flour you're obtaining in the US is different.