Is there a way to properly steel-cut oats yourself?
Seems like you should consider investing in a grain mill.

They come in a wide variety of options from manual to electric and they have different settings for how fine a grind you can get. While many of them may not grind as coarse as needed for cereals, there are many, particularly the manual mills, that do.

You probably want a burr-style mill... they're essentially the same thing as most pepper mills or good-quality coffee mills. Find one that does very coarse grain milling... perhaps check with homebrewing groups to see which they recommend, as milling is part of the brewing process.

I'm not sure you'll get the same results as a true steel cut, as it's a factory process but it will certainly be more consistent than your current results.