There is an amulet market where a huge selection of amulets are being sold. When I was there, I saw mostly locals buying amulets from there and literally no tourists. I have been told that many of the amulets were sourced from here.
Sometimes you have people buying amulets from here for a cheap price and then passing off to unsuspecting people that it is a special amulet, therefore selling the amulet for hundreds of times worth the original value.
No doubt, monks can buy the amulets from here and then bless them and pass them to their followers. However if you are receiving amulets from a stranger, then please be a bit careful ya.
The amulet market is located within the compounds of Wat Ratchanatdaram in Bangkok:
It is just opposite Wat Saket วัดสระเกศ (Temple of the Golden Mount).
Wat Ratchanatdaram วัดราชนัดดารามวรวิหาร
2 Maha Chai Rd, Khwaeng Wat Bowon Niwet,
Khet Phra Nakhon,
Krung Thep Maha Nakhon 10200, Thailand
Location: located at the intersection between Ratchadamnoen Klang and Maha Chai Road, in Phra Nakhon district, Bangkok.
Opening hours: 9am to 5pm
Entry fee: 20 baht if you are visiting the temple premise but free of you are browsing at the amulet market.