Finding Old House Plans

I’m considering making some medium-sized renovations to my Brooklyn townhouse (opening up a galley kitchen, adding a bathroom), and I understand that the first step is that I need accurate plans/blueprints of my home. I have no idea if there have ever been any plans drawn up of my house, but there was an extension added by a prior owner, so I guess their might be. Do you know: a) how to find out if there are plans on record anywhere with the city, b) if not, how much I should plan on spending to get some drawn up, and c) any recommendations for an architect who could/would do such work even if I might not actually do the renovation anytime soon?

Thanks,
CG

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