The only ones I know of are Bosun's Locker at Port Edgar Marina, South Queensferry and Seaspan in Granton (west harbour road), although I understand the latter is closing down soon. Bosun's has a good range of stuff, but as with all such establishments its not cheap!
Bosun's Locker is the only yottie one that I know. However, there's a chandlery in Grangemouth that specialises in diving gear and workboat/mobo sales: http://www.fym.co.uk/