I use the email which I got from the booklets: email@example.com
Note that Philip can be contacted on this forum, contact the user known as Greywolf, Greywolf has responded on the public forum so that appears to work.
Postal addresses: I have only tried this once and it was a long time ago.
BDO Midlands (Bardic Course)
Box 33 c/o Wildways
Borle Mill Bank
Shropshire WV16 6NJ
It’s a lot slower than email but they will respond.
There is also:
The British Druid Order
PO Box 1217
Wiltshire SN10 4XA