I would insist on Stainless Steel, Full Extension slides.
The standard lengths are 12' to 24" in 2" increments.
Not all Manufacturers make slides in all the lengths.
Don't waste time looking at the big box stores. They don't stock anything unless they can sell a couple of hundred every week.
First check for any local sources that sell to cabinet makers or similar trades.
You don't give your location but here in LA my best source is: http://www.andersonplywood.com/location.htm
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