Someone in our shiur claims to have heard that it is permissible to extinguish a gas fire on yom tov if it is done by turning off the gas from the main connection, since the extinguising of the flame does not occur immediately, but only after the gas in the line is used up. He believes that this was one of R Moshe Feinstein's tshuvat, but cannot recall where.
Have you heard this.
In three places in Rav Moshe ZT'L's Igros Moshe, Orach Chayim I (#93, #115, #128), he touches upon the Halachah you mention. In each place he alludes - or writes explicitly - that although he has is capable of providing a very lenient ruling on the matter, he would rather not commit it to writing. So I doubt that you will find it in the Igros Moshe, and even if was recorded in print elsewhere Rav Moshe may not have been so happy about it.