Wow!!

That's the motherload!

Quite a range of prices, too...

Regards,

Russell

https://www.menards.com/main/lighting-ceiling-fans/replacement-glass-shades/patriot-lighting-reg-clear-cylinder-replacement-glass/937001/p-105477937826-c-7509.htm

Not sure if this one has been posted before, but Menard's in the U.S. has a pretty decent-looking Fresnel-style lens available for under $30!

Interesting!  I had not seen this.  It looks like the ones Vermont Lantern sells (not an actual lens, just a glass shaped like the lens but with no thickness--still, the price is good and probably a little simpler than poring through the Vermont Lantern Website. 

Looked, but did not see anything large enough. Nothing at Menards, and Vermont Lantern only had one model at 6" diameter and it was out of stock. Lowes fixture was also out of stock. Am looking for something more like 7.5 inch diameter at the base. 8.5 inch overall diameter.

The "jelly jar" type porch lights are inexpensive here in the US, but pretty small, bottom opening if used upside down is about 3.5" diameter. Another option is to fabricate a mold and pour a polyester resin copy. Since others have kindly posted a dimensioned contour.

Since I'm here, I'll chime in with a possible solution for people on a budget that are content with "good enough" accuracy:  Large jugs of cleaners like Pine-Sol.  Can't speak for Home Depot, but Lowe's has like, gallon jugs of household cleaners that are about the right size and bear at least a passing resemblance to a Fresnel chimney.  Sadly, the one that is the closest match (imo) is green plastic, but most of them are clear.