I got some spotter bottles from solutions, they even custom printed the labels with my logo.
But to say the are a great marketing tool is misleading, they will bring in work but on a ROI they were one of the worst things I did, even if you add a couple of quid onto the price to pay for them they still don't work well. You could just add that £2 onto the price and keep it then spend the accumulated amount on marketing that works better..
If you look at the maths of it rather than just think 'it's only a £1 that's nothing' you buy a 100 that £100 you spent, how much return would you get if you spent that £100 on adwords or leaflets or a village magazine? I worked out that I would get more if I spent my money elsewhere.
Spotters do work for marketing but don't look at them with rose coloured glasses