Lindon Lewis marine . Its just past Walton Bridge on the port side , youll need to go into the cut just past the old ferry boats with pink hulls .
After that its petrol stations and jerry cans im afraid .
(dunno name) Outboard specialist just below Abingdon,
similarly boat hire firm just downstream of Abingdon bridge.
The prices are currently around £1.15/l, so if you've a small boat, you'll probably be prepared to fill from cans, in which case there are loads of filling stations which you can see from the river -
Total station on LHS as you approach Staines
Sainsbury's in Staines (can't be seen from the river) 300yds walk through office complex on LHS after bridge.
Immediately after Maidenhead bridge on LHS, even got some steps going up.
After those it gets a bit thin -
Cookham, Marlow, Henley, Reading, Pangbourne, Goring, Oxford all have filling stations but not what I would call "near" the river.
Just home from a week on the old girl going from Datchet to Abingdon - redline at Abingdon do petrol £1.15 a litre - coming back down stream in addition to those already stated - and I agree petrol cans are cheaper and essential with the lack of on water petrol (apparently the licences are the issue) Bourne End - stop at the Marina take a water fill up £1.50 and wander 500 yrds up he road to the high street and fill up the cans. Reading - moor at Tesco's on the river walk through and the petrol station is next to the supermarket 500 yrds or so max. Datchet moor near Kris Crusiers up the high street - turn left and Total station on the right (walkable).
There is a walkable petrol station across from Teddington Lock, ditto Hammerton's Ferry below Teddington. Hobbs of Henley do the stuff (second mortgage required) and there must be somehwre in Kingston. Staines Sainsbury's is near the river as well. Personal experience is that 500m with a full 6 gallon portable tank is a great way to longer arms. Folding trolley!
Petrol stations away from the river may look unhappy if you show up with anything other than the usual 5l plastic can.