Class Zz Minus Plug & Pin Gages - MSCDirect.com
The link above is for 0.451 pin. Just enter the size you want and add to the shopping cart. Six pins would be about $30 with shipping.
The SET I bought (250 pins) from MSC 0.250" to 0.500" by 0.001" increment was under $100 about 2 years ago. Today the price was ~$280. I bought the set so I could check anything from .25 acp to .500 Boomer.