Earlier, "Ernie" wrote

a friend bought a DART 17(T51 17R), build
in 1968, SN1610. Glider is in good condition
but the canopy needs to be replaced.

The only replacement Dart canopy I've ever seen was on Mike Hoke's
Dart. It was made by Cowley at El Mirage; they're long out of
business. My general experience is that the least expensive place to
get a replacement canopy is from the holder of the original tooling.
Doing it once with parts that fit is almost always cheaper than doing
it twice.

Two other resources to consider:

Thermotec (Ray Poquette) does one-offs like that, but can be a bit
pricey.

Jim Marske free-blows canopies for his Pioneers as well as 1-26s and
things like that. You might ask hem to help.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com