Banglamun Hospital blood bank or the Chonburi Red Cross mobile blood van comes to Pattaya. I recommend donating at a Red Cross as they transfer throughout the country. Let me find the Chonburi Red Cross mobile van schedule
Here are the hours of the National Blood Centre on Henri Dunant Rd. Near Sam Yan metro stop or Silom.
If you are from the UK, France or Ireland and lived there from 1980 to 1996, the National Blood Centre is the only location due to vCJD " mad cow disease". Special processing required for blood.
The other popular Bangkok location is at the Emporium Mall. Please Google this... I am not familiar with this location. I think there is a recent post where someone gave specifics, I will look for it.