Millets don't sell Lowa boots to my knowledge.
Ebay is worth a look. My boots of choice would be
these But then I find a high top boot more comfortable - which is not everyones cup of tea.
You might be able to find a Grade 1 used pair that you will still prolly pay £50+ for!! From memory the German army issue them only if the soldier has a foot problem - this might put you off a used pair
I also belive that the German army used "Lowa" boots are made are made by 4 companies including Lowa - so it's pot luck that you will receive actual Lowas
But on the plus side they are all made to the same standards - although there are some slight design differences.
Have a look at the used boots on ebay
here
Hope this helps.
Phil.