Need COTS Analog Speed Signal from Encoder

Hello everyone, need some shopping help. 

I have a customer who wants to get a scaled analog output corresponding to rotational speed from an encoder instead of doing traditional freq measurements.  We want a stand alone package that does the frequency measurement on board and just puts out a scaled analog output.

Need < 100 mS latency and ability to resolve 5 rpm to 1000 rpm.  Just don't know where to go to buy one.

Anyone know of such a device?

Thanks 

Wes Ramm