Buying Minoxodil in UK - is it easy? Where is a reputable place?

Dear All,

Good morning/afternoon to you all. I am hoping that this wealth of collected knowledge will help me.
I have been using Minoxidil 5% and Azaleic Acid 5% for about 3 years via a Hair Loss Clinic and am near the end of the 3rd year of treatment. It has definitely worked however I would like to maintain my own treatment mainly because its incredibly expensive (£600+). In your collective opinion -
1) Where can I purchase Minoxidil from that ensures it is a genuine product?
2) Does it matter that the solution would not contain Azaleic Acid (i understand this is a weaker DHT blocker) so would the loss make any difference?
3) Is it worth using Nizoral Shampoo instead of the “prescribed” shampoos/conditioners instead?
4) Any other advice?
Thank you so much in advance.
Voxiana