[Arran]

Another option is to use a later 3 volt battery tube like a 3Q5, and connect it as a triode rather then a beam power tube, this is basically where you tie the plate and screen pins together. I'm not sure of the interelectrode capacities verses a UV199 though but the tube manual will give some guidance, all it would take is a small 4 pin to octal adapter, or loctal if you prefer a loctal version. At least a GT or G style 3Q5 will look somewhat like a 199, without trying to make a fake envelope, which gives them the look of a fake tube amp from the "Middle Kingdom". UV199s, whilst not as common as 01As, are not like WD11s where they will fail if you look at them sideways, resoldering the pins on an existing tube is also worth a try if it tests poorly.
Regards
Arran