You should use a referee from where you are volunteering and put your last employer. Do they have HR there? Just put that. After 12 years all they might be able to do is confirm dates, and it would be unusual to get more than that anyway from a job that long ago.
I've just put in an application for a job at DD's primary school and am currently in my second year of volunteering there so hopefully that will suffice even though I don't have a written reference. I've also volunteered in the past as well. I'll have to get in touch with my last manager to ask if I can put his name down as a referee.
If he will allow you to list him as a referee it shouldn't matter as much if you don't have the actual written reference. Some employers will prefer to speak to him anyway. You should always have your last employer down even if it was a long time ago. In a similar situation I got someone else to be a character reference for the second one. It was a neighbour for me but anyone professional who knows your recent character is acceptable. You can explain your reasons for your choice of referees in your covering letter if you feel its appropriate.
When I resigned from my last job after the birth of my first children I forgot to ask my manager for a reference. I asked a couple of times during the next couple or years but he never sent it. I resigned 12 1/2 years ago when my boys were 6 months old.
Now, I am about to start applying for work but have no reference. Even if I did have one it would be over 12 years old and not relevant to who I am today.
What do I write on applications under these circumstances? Who could I suggest to prospective employees that I use as a referee?