May 2nd is the next one I know of.
IIRC, it's usually held at a union hall in the I-696 / I-75 area.
Check out "ipms warren or ipms livonia" for more details. "Semmex" is what they call the show/contest.
I haven't been in some years, but there was also an annual show up near Bay City (MidMichiganModelMakers), late winter / early Spring-ish. Last time a went (couple few years ago)...it was at the National Guard Armory, just off 23.
I completely forgot this year, but there's a show in Kalamazoo (at/in the air museum)...1st or 2nd weekend of October.