The Captain Johnson, whom Tom mentioned in connection with Tregelles's Three Letters, was Captain (later Major) Richard Courtenay Johnson who supported BWN and was a trustee of the Compton Street chapel to which the remnant of the Ebrington Street assembly relocated in Midsummer 1848. There is a copy of his The Point at Issue (replying in 1848 to JND's Remarks on BWN's Letter connected with our Lord's humanity) in the CBA in Manchester. He was born c1802 and had been an officer in the 50th Regiment of Native Infantry but was invalided out in c.1838. He died at Arcachon (near Bordeaux) in France in 1869. His daughter Charlotte ('la Signorina Carlotta") was active in the 1850s and 60s among the Brethren in Florence where she died and was buried in 1869. Timothy Stunt
Here is the location of addresses by William Johnson/W.J. in the Believers Friend. Vol.9- Recovered for Gods Pleasure pg 64: Vol.9- The Law of the House of God pg 116: Vol.9- The Priesthood of Christ pg 176: Vol.10- A New Generation pgs 172 & 204: Vol.10- Our Place and Portion pg 63 (correction in relation to this address pg 112) : Vol.11- The Perfect Servant pgs 5 & 34 That's all I could find? But the friend who is searching WoGaE for you may also have copies of TBF?
This page gives details of his son who died in WW1, and also a picture of his grave.