Hi John,
Welcome to the forum which I hope you will find helpful.
You have made a good start by Getting John Lamberts plans.
The only fittings that I am aware of that you may find useful are 1/24 available from
http://hslmouldings.co.uk/index.htmAt 1/24 you looking at a model 55" long with a total weight of 9.2lbs plenty of scope for two engines etc if you should require them.
At 1/35 (Military Modelling scale you may find some bits and pieces), you're looking at a model 37.7" long with a total weight of 3lbs. The available weight is whats going to cause you problems as its going to be difficult in my opinion to be build down to this weight especially as its your first boat. We all tend to over engineer models.
What period of the war did your father serve on her? They started out as minelayers and later changed to convoy escorts and this will effect the weapons carried.
John Lambert also produces a book called 'Allied Coastal Forces of WWII Volume 1" . This book covers the Fairmile A though there are no pictures of ML104. There are only ten pages much of which is drawings I suspect you allready have but worth getting a copy from the library or perhaps secondhand.
Hope this helps you on your way,
Regards
longshanks