hmm...that could be difficult to find a speaker that only has midrange.
you could
1. buy a component and not install the tweeter (your idea above)
2. bite the bullet and buy a coaxial and have a little less low end...

i know it sounds crazy, but i have a pair of old boston acoustics (component with the separate tweeter), that i would be willing to send to you for $20+shipping... the reason for the low cost is that they have no crossover so they dont sound good right now (they are trying to produce high freq. out of the woofer)...
i only have the woofers, no crossover and no tweeter. they are older, but they still sound ok. you would just have to find an inductor at the right Hz to eliminate the high freq.