Phone the RYA legal department and ask a nice lady called June to email you the Word version - she did this for me a couple of weeks ago without asking for membership details, although I had previously joined anyway.
I would send it to you, along with the the Agreement, but that laptop has finally died a death /forums/images/graemlins/frown.gif
I'd recommend that you use the MCA form of Bill of Sale, even if it does seem OTT. The form of a Bill of Sale is laid down extremely specifically in the (now very old) legislation. There is a risk that what you think is a Bill won't take effect as one, if you depart from the statutorily-imposed form and content.
Using the MCA form is a good way of ensuring that all the boxes get ticked for compliance with the Acts.
Copyright issues aside (I am not sure if the MCA bother with that though) it is quite acceptable to print off the PDF supplied by MagnaCarter and just write in the details (or, should you still own such a thing, use a typewriter and type in the blanks). PM me if you need help completing the form.
The form provided by lescargot is the form of agreement of sale - the document that you and the other party sign up when the deal to purchase is first made and the deposit is paid over. It's a perfectly good form to use at that stage, but you will still need the Bill of Sale when you complete, i.e. when the balance is paid and the keys are handed over.
Just as a follow up, I see that one of our law textbooks in the office contains copies of the RYA sale contract and the RYA Bill of Sale, up to date as of June 2006, together with commentaries and drafting notes. The Bill of Sale is for unregistered or SSR yachts only and is a little simpler than the MCA form. PM me with an email address if you want me to send it over (PDF only).