I am attaching a photo I have had stored on my laptop for ages of an actual June Tailor Clapper, and it has the instructions for use on this.
Whilst I do not have a clapper like this I do have the June Tailor Tailor Board and also a separate June Tailor clapper and point presser combined.
As you have found all these items are difficult to get these days, the Tailor Board probably only via e-bay, however the clapper and point presser combined is available through two places here in the UK that I know of – The English Couture Company up in Syston Leicestershire, or via Sew Direct down in Havant. They are not cheap, but once purchased it is a really essential piece of sewing/pressing equipment.
The Tailor Board, the clapper and then the clapper and point presser combined were possibly the most popular items made for dressmakers by June Tailor’s company, however when she sadly passed away for some reason the company stopped manufacturing these much to the dismay of many dressmaker apparently they had been June Tailor’s most popular items sold. I have heard that some people have managed to find a carpenter who is willing to make these items but at what price.
Occasionally these items do come up on e-bay at a ridiculously high price but they are worth it. The Tailor Board used to come with optional covers, a very coarse cotton type fabric that has been fused to some foam, again these covers are sometimes found on e-bay.
At one time June Tailor produced a booklet A4 size – 22 pages called The June Tailor Method of Custom Detail Pressing, this covered plain seams, flat felled seams, French seams, simple darts, pointed darts, dress maker’s darts, slashed darts, lapels, interfacing, round collars, pointed collars, set in sleeves. There is a whole page devoted to the June Tailor basic pressing equipment which consisted of the Tailor Board, the Clapper, the Sleeve Board, a contoured dressmaker’s ham, a ham holder, a Tailor ham, a seam roll, a Velvaboard, a Point Presser/Clapper, a pressing mitt, a cushioned pressing pad, a Press Mate ironing Board cover, and various pressing cloths. The booklet then goes on to show you how to do the pressing using these various pieces of equipment. My booklet I found possibly through abebooks and came from the USA.