Flash tube for OLD (ancient) Ascorlights is GE FT-506. A good approximation is FT/86. It needs to have the base fiddled with, but the specs are the same (900 volt, 1000 watt).
Here is a URL to a picture of the Speedotron MW3QVC which is their FT/86-UV. Also in the catalog as Speedotron 24570. http://www.bulbman.com/browseproducts/FT86-UV.HTML Bulbman stocks them at about $87.
Here is a URL to a picture of the GE FT-506 used in the ancient Ascor...
http://donsbulbs.com/cgi-bin/r/b.pl/wk-506.html This is from Don's Bulbs.
The two major differences are that the FT/86 is shorter and the FT-506 has a center post (true octal socket). There are two possibilities... Either use the FT/86 without the key (very risky), or make an adapter out of an octal plug and an octal socket. Done right this can put the length back.