Please, I need ASIN Number Help

I am after some advice from my fellow users.

When I find an existing listing that I can list my products against, lets take this one for example.

https://www.amazon.co.uk/Gildan-Cotton-Sleeve-T-Shirt-Military/dp/B00ZQ6N4EM

I can click on each colour and size individually and then Copy & Paste the ASIN so I can bulk upload list once I have all of them.

Question 1: If the colour/size is listed as out of stock, I cannot find a way to get the ASIN which seems absolutely crazy to me, (example, Military Green in Large) just because no other seller has it available, doesn't mean that I don't, but without the ASIN I cannot add it on.

Question 2: which some of you may be screaming at me, why am I doing it this long way. Is there an easier way to extract the ASIN information from a listing for all the colours/sizes in one swoop as some listings are huge, 50 colours, 7 sizes 350 ASINS.

I'm sure that I am missing a trick here and would love to hear your advice.