Last Updated: Aug 26, 2016 Views: 76
I believe you are describing "crown glass" windows -- they have a thick central section where the glassblower's tool was attached. We call it the "bullseye."
The technique, and other hand-blown window techniques, are described in the London Crown Glass Company website: http://www.londoncrownglass.co.uk/London_Crown_Glass/Manufacturing.html
Stained glass suppliers often carry this type of glass. Take a look at the UK Stained Glass News website for a list of suppliers and/or manufacturers (worldwide):
They also list UK studios -- you may find someone locally who can suggest a supplier.
It may be possible to commission a glass artist to make "nipple glass" for you. The Contemporary Glass Society can help you find glassblowers: http://www.cgs.org.uk/