How to optimise gold purchase using cc?

I want to purchase 20gms gold for my mother to make some jewellery. Local jeweller said give cash I won’t charge GST but I’m not in favour of black and would like to do some legitimate purchase and then just pay making charges to some jeweller of my mothers choice.

So the total spend will be \~3lacs so how do I optimise this purchase so as to get maximum returns? Buying amazon gift card on using SBI cb gives 5% but is capped at 4K so 80k worth I can buy in a month. How do I accumulate rest? Should I simply use HSBC T1 as it will also go in annual spends milestone and earn me some reward points?

Cards that I have - HSBC travel one, HDFC millennia, sbi cashback, icici Amazon pay.

PS - I was also thinking of getting some other card maybe HDFC bonvoy just for international lounge as I’ve exhausted 4 on T1 card and need more by end of year. So if I should make these spends there I’m okay with that or with another card.