They should all be available in NY but I am not sure about the prospects of putting vinyl replacements in aluminum framed double hungs.

you mean your not sure about putting vinyl where aluminum was? whats my alternative? or do you mean not a good idea switching the sliders to DH?

That's a really odd size to use a double hung in. Double hungs are usually taller than they are wide. If you are looking at double hungs because they are easy to clean, Sunrise makes a swing slider that's really nice. You should be able to get Sunrise in NY.

Here is a link that might be useful: Sunrise Slider

I was choosing double hungs just because I like their more traditional look. Whats your opinion on sliders vs casement. I'm assuming casement is the better window but is it crucial ? I've heard of all the window styles sliders are the lowest quality, I'm guessing the worst "seal" when closed?? My gut is telling me not to go with DH, but do I go with the more expensive casement or will sliders be just as good?
and do you have an opinion on silverline?

I do not know if you can put a replacement window in your window. What type of frame do your current windows have? If it is a 2 3/4" frame a replacement unit might not work. Silverline would be considered a poor window by most any professional in the industry.