Which variant are you playing? With (144 tiles) or without flowers (140 tiles)?

If you play without then you can order a riichi set from Amazon JP and that will work cause it has the season tiles, but no flowers (has 4 red five dora tiles instead)

For example: https://images-na.ssl-images-amazon.com/images/I/71Jb6l0E%2B-L._AC_SL1333_.jpg (as you see no flowers, instead comes with the red five dora tiles)

Amos Max is one of the highest quality and recommended generally https://www.amazon.co.jp/-/en/dp/B015SDE3SS 28mm, 16gr heavy (iron cores). There are another 3 versions too (same size without iron core and a smaller size with and without iron core)

I have an Amos set from Amazon JP and arrives to Europe quite quickly. But the shipping + customs adds another ~100-120% to the price. Basically you pay double. But well worth the money!