You might find some relief with one of these units:
TENS Unit – TENS and Muscle Stimulator – TENS Muscle Units
It is both a TENS (transcutaneous electrical nerve stimulation) and EMS (electro muscle stimulation) unit. I bought one of these particular units years ago for intermittent muscular pain. Thus I have only used the EMS half of it, not the TENS half. It is very good for cramps, spasms, back and neck pain. The EMS function stimulates your muscle and causes it to contract, relieving spasms and such. The EMS part can be made to feel similar to a massage. Besides a bunch of ramping, timing, etc. settings there is an intensity setting. That intensity setting goes from "can't feel it" to "rather nice" to "barely tolerable" to "you've got to be kidding me - this is like a TASER". The unit is highly adjustable!
The TENS part works totally differently. It sends electrical currents across nerves, confusing them, and thus helps with pain (I guess the nerves cannot transmit the pain sensation in this case). You would probably need advice from a physical therapist on the correct settings for TENS usage. And the correct placement for the electrodes. The EMS part has tons of different settings as well, but for muscle help, pretty much you can just experiment and see what works the best for you and the given situation. The EMS settings are not as specific as the TENS settings. You may be able to find info on how to set things online as well. The manual tells you
how to set things, but it doesn't tell you
what to set them too - it says to contact your physical therapist.
You can buy replacement stick-on electrodes, in varying sizes, on Amazon. Of from the retailer above.