You can get all the Biotest products here: www.Biotest.co.uk but you probably won't like the prices. AFAIK some people are actually ordering directly from Biotest (US) because it's cheaper to pay for shipping.
As far as I know there is no real replacement for Anaconda available anywhere. You can do pretty well with other stuff, though, including some easily available in the UK. It won't be the same, but it will be a lot cheaper.
The 10 to 20lbs part is just a result of a quick copy and paste job. There are in fact a couple of errors in the sheets provided. When in doubt go with what the video is showing. You'll see that 10 to 20 is generally what is added for barbell exercises. For dumbbells you would usually go up 5 to 10 pounds (spread on DB rows will obviously be greater than on lateral raises).
Most dumbbells I've seen in the UK so far are made by the same company (Escape I think?) and have a 2kg jump. If that's to much for you you can always improvise - for example spend a couple of quid on two pieces of chain, each weighing about 1kg and attach them to the DB or your wrist.
The most important thing is to go with what feels right. Pick a weight that does not feel too light for the first set and go up so that the last set is very challenging.