There are several aftermarket sources for tops- most have glass-window
tops that will fit your car. The tops are quite different because the
inflexible glass window is smaller than the flexible/unzipable plastic.

Robbins is a well-known brand, and makes tops in several grades (as well
as a wide price range- from <$300 to over $750)

Glass windows usually have defrost; if your car doesn't have a defroster
line (those sold with factory hard tops should), it's a pain to install.

Check miata.net for top vendors, explanations of the replacement
process, and other information.  I'll leave it to others to explain how
hard the job is; I'm fortunately still on my original top.

Joe
Silver '99

Check this URL

http://www.miatamania.com/Browse/SubcomponentMenuProducts.aspx?WebCatalogID=14&P
lateTypeID=1&ComponentID=17

they have glass top windows, I recommend whatever top you buy that you get
it with a rain rail as this simplifies installation.

Check recent posts here and on miataforum.com about various choices.
Also check the product reviews on miata.net.  The Duetto no-zip glass
top has gotten a couple of favorable reviews here.  I would not like
to have a Robbins top since when down they lay much higher than
stock, destroying the sleek lines of the Miata in my opinion.  If
you do not care about the looks, they are very good quality tops.

I installed an M2 top on my Miata,
http://www.bigbendmiataclub.org/bigbend/events/051902/index.htm
but they are expensive even used, because of demand.

Leon