Recommendation Letter for grad school without academic connections
This is the sort of question that can only be answered correctly by an individual university. Some will interpret such rules very strictly, others not so much. You can, of course, inquire directly with either the admissions office or an individual academic department, giving your situation. The feedback you get should guide you and help you avoid some of the frustration. 

However, as you do that, you can also try to re-establish the relationships you once had, in person if possible. You may be surprised and some of the people may remember you and wish to help. This reestablishment of old relationships is a good thing in any case and people may be able to guide you further. 

The comment of user Stella Biderman about industry letters is also correct and will help in most cases. 

Another avenue that might be open to you, however, is to actually approach a faculty member at one of the universities you would like to attend. You can most likely learn their office hours from an administration office. Show up, perhaps having first sent a letter stating that you will, and talk about what you would like to do. If you can interest them in you, they might be able to ease your way. 

Faculty members are busy of course, so make any such meeting at their convenience and be ready to state your goals and make your case succinctly. Again, you are likely to get further advice, rather than a brush-off. 

In general, I think that unusual situations don't fare well unless unusual measures are taken. If you just meld into the crowd you won't get any "special" consideration. 

There are likely a lot of others in similar situations. Find a way to stand out a bit from the crowd.