I placed an order for a substantial number of Size 4 glassines with Subway Stamp Shop back in July. It was on back order all this time. I've spoken with the people at Subway every 2-3 weeks to check the status of the order. The delay was because the manufacturer was having equipment problems.
Yesterday, I received an email cancelling the order. The reason is the the manufacturer, MeadWestvaco, is no longer manufacturing glassine envelopes.
I've been able to find a supply which, hopefully, will fill my needs forever, at least that is the dream.
I'm unaware of any other manufacturer of glassine envelopes in the USA.
Has anyone else run into difficulties obtaining glassine envelopes?
Just search glassine stamp envelopes and you will have a very long list of dealers selling everything glassine. That is probably just one company not bothering with manufacturing them as demand may not be as great as it used to be. Used by many for much archival material preservation as well as stamps, photographs, negatives etc.