Rory - Here in the states in some stores they sell aquarium kits that come with everything for the tank, the filter, a how to book, they are really nice. I first started out with one and then eventually upgraded to a 4 foot tank with a Rena 75 gallon Canister filter that works beautifully. You're having trouble finding tanks, but perhaps you can find one online? There are even some tanks that have the filter/power house built into the cover of the tank, but I have used one of these, and personally they do not work as nice.
If you can find a nice tank and you want two axolotls, make sure there is room in their for two axolotls. My first tank I had three juvi axies in, and I had been planning to upgrade. In smaller tanks, the less space the more likely the axolotls are to nip and bite at one another. I had a white female who was constantly nipped at or picked on by her two tank mates for a long time. I had to keep removing her, but as soon as I got that 4 foot tank which is perfect for 6 adult axolotls, she became the dominant female lol.