First I'll say that I got the idea from a guy on TBN (who got it from someone else on there) who also had a youtube video on doing this. I'm pretty sure he did it on a BH76 so you may want to check that out.
These are some of the parts I used that would also work for you:
Valve:
http://www.clearwaterhydraulics.com/index.php/hy-sv10-24-0-n-00.html
Solenoid:
http://www.clearwaterhydraulics.com/index.php/valves/by-type/solenoids/hy-6956093.html
Valve body:
http://www.surpluscenter.com/Brands/Hydraforce/HYDRAFORCE-SERIES-10-2-WAY-HOUSING-7024260-9-7024260.axd
I had to buy those three parts separately since I couldn't find anyplace selling them as a package. You can get different wire connections on the solenoid and different threads and sizes on the body, the link below has links that will give you the different part numbers. If you go with the solenoid I used you'll need to get the weatherpack body, wire connectors, and seals to make the connection on the other side. I got the weatherpack because I wanted the ability to disconnect it if necessary, and I wanted that connection to be weather resistant.
http://hydraforce.com/Solenoid/Sol_html/1-064-1_SV10-24/1-064-1_SV10-24.htm
Switch:
https://www.zoro.com/cpi-weatherproof-switch-push-button-b7151-516/i/G1687077/
Switch housing:
https://www.zoro.com/cpi-back-switch-housing-hs002-502/i/G2506445/
Kind of pricey for the switch but anything else would have probably been too bulky to mount on the joystick and/or not weather-resistant. Once I tightened down the zip ties with a zip tie gun it stays in place pretty well. I also added a SPDT toggle switch that can switch from "on all the time/off/controlled by the push button" but I don't really think that's necessary and I probably wouldn't add that if I were to do it again. I got power from the implement wires at the back of the tractor. They are a keyed power source so that works out well. I installed a 12V power plug (cigarette lighter socket) so that it can be detached easily when I take the backhoe off.
The hydraulic fittings on my backhoe are 1/2" JIC. I just put a tee where they attach to the bucket cylinder. You've got to mock everything up and then see how you want to run the hoses, measure, and order them and whatever fittings and adapters you'll need. You've also got to watch out for clearance on the fittings on the thumb cylinder, I had to remove some material from the thumb to add clearance, and turn the solenoid valve 90 degrees from how I wanted for clearance on the boom.
I don't know the size of the pins on the BH76 but on the BH92 the upper thumb pin is 1.25", so I struggled to find a cylinder that would take that size pin and wasn't too large of a diameter. The one I used was from a place called Magister Hydraulics and was listed under "Loader cylinders". Bailey's Hydraulics had the same thing listed but was out of stock when I ordered.
If your pins are 1" or smaller you should have no problem finding any number of cylinders that will work. The other pin on mine is 1" so I had to make a bushing for that end. I also had to use some washers as shims on the sides of the cylinder ends.
It really was a bigger project than I anticipated, but it was still a lot cheaper than the OEM hydraulic setup, actually around the same cost or a little less than just the OEM cylinder. I think I also like the push button better than I would a foot controlled valve. It would be nice to be able to control the thumb independently, but this works just fine.