deHavilland Mercury Type 85 tubes - Help needed

One of the two Type 85 output tubes of my deHavilland Mercury preamp has died and am unable to get a matched pair of these tubes or a pair from the same manufacturer. Tube depot, Tubeworld etc.. don't these in pairs or matched.

All i can find is used single units on ebay.

I would very much appreciate your help and advice and also whether there are any substitutes i can use and whether its OK to mix different brands.

many thanks
Have you asked Kara Chaffee at deHavilland?
Yes I have sent her a mail today itself and am awaiting reply.
I thought that you said that you could not get the tubes from the manufacturer - that is Kara Chafee.
What I meant by the "same manufacturer" was of the same brand i.e a pair of Type 85 of make Sylvania, RCA, Raytheon, Delco etc.. Kara Chafee does not manufacture tubes.
Sorry, I thought that you were speaking of the amp.
I finally got a few pairs (RCA) on ebay. cheers
I have bought tubes from here a cpl of times. They seem to have a little of everything.