We just bought one from Sandhill Preservation in Iowa. They only sell straight run chickens, in groups of 25 - you can mix breeds in an order. They are sold out for 2019, but you could order for next year. I think they accept orders for the following year sometime in Dec. Our little Redcap is 6 weeks old now, and seems to have a friendly personality - I think she is a female. They have many breeds that are on the conservation watchlist.
You can do a google search as there are a few hatcheries that sell them. However, sometimes with hatchery stock, you may or may not get a good breed example. A google search gave me a few results.
Of course, you can search the NPIP website. By state:
http://www.poultryimprovement.org/statesContent.cfm
They use stock codes, on left side of the above link. Here is the code for Redcap:
View attachment 1810476
You can open the state Doc (for example Texas has 25 pages of NPIP breeders and hatcheries), and then use your "find" function on your computer to find "R125"
Unfortunately, TX did not have any results. So, look at the states near you (if you are near another state) to see if anyone there carries them if you wanted to pick them up.
We ordered from Sandhill and paid for express shipping. We received the chicks in OH, just 17 hours after the PO in Iowa received the package.
Good Luck!