I'm sure you have tried this, but craigslist is a great resource. I have seen on numerous occasions people selling or donating their sinks in the tri-state area. Having said that, the sizes often do not correlate to the space you have available. If you need a custom sink, I would try a custom steel sink fabricator because they can create a new sink to your design in less than a week. The trouble is moving it if it's large and getting it in the space...and also you have to design it. It's also generally cheaper than the businesses selling industrial sinks. In Brooklyn (bushwick), I know a fabricator who builds for chemistry sinks for schools and has built sinks for darkrooms in the past.