This may help
http://www.applianceaid.com/garage_fridge.html

I need help to get my garage freezer to work.
First is it a freezer or a fridge. Further on you mention a fridge.
Also is it frost free?
From what I have found this is the kicker on fridges.
The unit goes into a defrost mode. This generates heat in the unit but because the ambient temp is low (the fridge section does not warm up) so the compressor does not start up after the defrost and everything in the freezer section partially melts.

I was told I could use electric heat tape around the compressor to fool it into thinking its warmer.
Do not understand this. Both freezers and fridges do not monitor ambient temperature so I do not know what they think they are fooling.

Guy at home depot said NOT to do this. I see the GE makes a repair kit for this sort of thing, but I have a Magic Chef and there is no part they make. Any ideas? thank you!!
If the problem is the compressor oil getting thick then this should work but you have to use the heat tape which has a temperature sensor built in (type used for copper pipes). Also where you place the sensor may be important you do not want to over heat the compressor. Do not know if you can get one that is short enough.
A battery blanket might also work, much lower heat output. Check to make sure that it has a thermostat built in. Some do, some don't.

Hopefully someone else has some better ideas.

Well I did find this for a Frigidaire, probably the same one you found.
Part Details - FRIGIDAIRE Garage kit, part number: AP3722172

But is says it is only good till down to 34 degrees.

Sorry I cannot tell if it would work in a Magic Chef.

Looks like they are adding some heat to the thermostat area so it will cycle the compressor on/off this would work but it is a balancing act re: if too hot the unit would run continuously. You still have the problem of running the compressor in a freezing environment which is hard on it and greatly reduces it's ability to compress the freon/gas.