There must be some demand for post-op MTFs, and looking at it from one angle, there is going to be less competition. But it is a horrible position to be in: either be honest and get less work, or conceal this (as Anika Mae says, with new everything) and risk someone taking his otherwise laughable insecurities out on you.
Is aiming more at pro-domme work an option? You already list water sports and 'light bdsm' as services, and many people into BDSM are less fussy about the gender of their partners.
They all have slightly different angles and attitudes (some think sex work is unspeakable, for example, but I cannot remember which) but have a look at spectrumlondon.org.uk, translondon.org.uk, transgenderzone.com, gender.org.uk, gendertrust.org.uk, and transliving.co.uk.
Specifically on sex work, my ex-work, now calling itself SWISH, may be some use: see tht.org.uk.
It's a pressure group rather than a support group, but the one I'm really jealous of is pfc.org.uk