If you want to go military style the WWII T-17 tank/aircraft lollypop handset caught my eye , around 25 dollars gets you a brand new old stock unit , complete with 3 pole BPO jack .
Looks like it would make a neat harmonica mic , although the momentary action two pole switch would be redundant , incorporating a mini volume pot in place of the switch might be another possibility .
Probably requires a polarisation voltage if its a carbon element .
This clip from Iggy and the Stooges has the kind of urban street megaphone quality on the vocals Im taking about , watch out for your hairpiece ,