Hi,
I had the same problem, finding the blue tinted bulb was impossible (in Ireland and UK).
So since I worked for a stained glass company I had a good knowledge on different coloured glasses.

MY SOLUTION:
dark blue water glass (that's the name of the glass, you can get it at the nearest stained glass workshop)

It is thin, and cracks from the heat but I sliced it up to four pieces and this way it stands the heat.
You can also get it toughened (tempered) but it's expensive.

The result is bright white light (although the blue glass shades the light a little)