Vintage Tube Services/Andy Bauman.
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I can recommend one very highly. It's the Tung-Sol 5U4-G. Look only for the ones with these attributes:
2. Top flash-getter.
3. Support rods between the plates.
4. Heat shielding material in the base.
You can copy and paste this link to see a photo of one (it shows everything but the top flash getter):
They are getting hard to find, but it's not impossible.