Anybody know where to get FRESH beef sweetbreads?

Hi! I know this type of thing is better suited to the boston-online forums, but since they are suspended I thought I'd give it a shot here. Sorry if this is inappropriate for Universal Hub.

So I need to get my hands on some calf thymus, otherwise known as beef sweetbreads. I'm not going to cook it, although I found lots of recipes online. I need it for immunological research. [The thymus is one of the most important organs in the immune system.] Since I need to purify proteins from this stuff, it needs to be really FRESH. Definitely NOT frozen. Best case scenario: straight from the slaughterhouse.

I spent some time this afternoon doing an internet search for Boston-area slaughterhouses but came up empty. My current plan is to go over to the butcher shops near Haymarket and ask them for help.

So, anyone here know anything about this? Thanks in advance!