The BU508AW is only available in the semi-insulated TO-247 and is still in production.
However, it was developed for CRT TV at the time and the number of such projects has now shrunk drastically, so there is no reason to develop a comparable or better alternative. The BU508AW is thus the only npn BJT that STMicroelectronics has on offer in this package and with at least this VCES.
Thanks for getting back to me and yes it does answer my question, but are any available anywhere to purchase. I've tried RS and Farnell but they have no stock and none expected till November. I need six ASAP.
I am very sorry to hear this, but the community is intended only for technical discussions that may be of interest also to other users at a later date. Availability is always temporary and must please and can only be clarified with the preferred or local distributor.
If the problem is solved, please mark this thread as answered by selecting Select as best, as also explained here. This will help other users find that answer faster.