Chorizo sausage as a ground chorizo substitute?

I think your best bet if you can't find any Mexican style (raw) chorizo (either loose or encased) is to just use some ground pork and add spices - the spice list on that product is:

chili pepper and less than 2% of the following: pork broth with natural flavorings, salt, dextrose, garlic powder, flavorings, spice, oleoresin of paprika, BHA, propyl gallate, citric acid.

So there's not much to add or find a recipe so you don't have to guess. There are a couple of them. Or just add a packet of "Mexican seasoning" to the sausage. I think this will actually take quite a bit less time than trying to prep Spanish style chorizo.

You're literally just mixing in some spices.

If you don't want to buy the spices, just switch to any "spicy" raw sausage. For example Jimmy Dean Hot. Again, this will be an easier option for you than using Mexican (hard) chorizo.

Assuming that the "chorizo sausage" that you are referring to has some manner of skin on the outside (and is "Mexican Chorizo" - see comments), you can do what I have done on occasion, slice lengthwise down one side of the sausage and turn it inside out, and discard the skin. Voila, instant 'ground chorizo'. You might need to squeeze the sausage together and then break it up as it cooks, but it should work out fine.

In one case (with Italian sausage links) I had to run the meat through a food processor for just a few moments to thoroughly break apart the sausage form, just don't over do it if you need to do this.