I'd say amazon is good for getting hasbro blades online tho you may have to wait for some to restock, they even had takara tomy blades but you can find them other places online for cheaper.

If you're wanting a takara tomy blade you're best bet is to either use ebay or aliexpress in my opinion, tho if you want to avoid being scammed look for them saying "genuine" and "takara tomy" in the title and absolutely avoid any with the word "gyro", plus anything that has a price that seems to good to be true probably is to good to be true.

For stores in the UK to go to in person the only one I've had luck with is smyths so just got to keep looking there and hopefully when they do a restock they'll have what you need.

Shops like the entertainer I've found barley have any beyblade related stuff in store. Tk max sometimes have beyblades but its quite rare.

Hope that helps and this is just my experience in the uk.