Ironically brown algae is often a result of a lack of lighting rather than too much, or to put it another way it can grow well in very dim light so lighting might not be the issue here - green algae usually thrives in tanks that have a lot of lighting, not brown.
As james15 alludes to, it may be excessive nitrates in the water causing the algae, do you have any live plants? If not, may be worth adding a few as they help absorb nitrates and can reduce algae growth. Also, try reducing the amount you feed the fish or reducing feeding times to once per day (if you feed more often than that).
Also, frequently vacuum the gravel to remove waste particles and when you do water changes keep it to 25% per week as replacing more than this in one sitting can contribute to algae growth especially if your water is high in nitrates anyway.
I get a fair bit of green algae but I use a lot of lighting for my plants - the plants grow well but I get green algae, that's the pay-off.
Great_kahn is right, you will struggle to find decent retailers but they do exist - thing is though we are kind of "out of season" for fancy goldfish, the best time of year to start looking for fancy goldfish is early Autumn, say around Sep / Oct time as this seems to be when the retailers get their best stock in.
I know it's out of your way but Wharf Aquatics in Pinxton, Derbyshire is excellent, I paid a visit a couple of weeks but their stock is pretty low on coldwater fish at the moment - I've heard Star Fisheries is also very good, they have open days but the next one isn't till September.
I have the same problem with my tank, it has no hood, just Perspex sliding covers - I can't fit my bulb to the back of the tank though as the water level is too high.
I decided to construct a light fitting for it so I bought a piece of white guttering from B&Q complete with end caps, spray painted it brown (to match the cabinet) and have fixed the light into that and it works a treat.
I agree with your point regarding the blue lights, I'm not a massive fan although it can be quite nice at night provided they are dimmed down considerably.
I still don't have plants yet (still at setting up stage) so I can't comment on plant growth but my understanding is that the LED's emit the correct wavelengths so it shouldn't be an issue.
Have you tried contacting local fish stores, preferably ones that specialise in fancy goldfish?
I had to re-home one of my Ryukin's that was becoming v aggressive towards my Oranda's, a local fish store took him and he found a good home.
Many are reluctant to take fish in as they normally only deal with designated suppliers but if he/ she is really healthy and has no problems then you may well find one that will take them off your hands, just don't expect any ??? though as you won't get any, remember they're doing you a favour.