Google is your friend.
https://www.google.com/?gws_rd=ssl#q=replica+matchlock+musket
You can get a non-working replica for about $125
Around $500 will get you a working piece.
Thats if you go for an authentic piece. I couldn't find any crappy plastic versions besides what they sell at civil war reenactments.
That is whats kinda cool about 18-19th century firearms. Most of the machinery used to make them is still around, and is used to make replicas(or rather just make new ones)