It will add a nice touch to your invitations and you can easily find somewhere they will custom make it for you. I found a cheap dealer on Ebay and chose R and C - our initials for the seal.
It took some practice with the amount of wax and what pressure I should use, but in the end it turned out very well and will be put to good use when we make our invites. The red wax was bought in a hobby store and they had a size that fitted my glue gun so it wasn't difficult at all to control the melting. You can choose to melt it in a spoon over a flame instead, which is the original way to do it.
In the end you add a nice touch to your envelops like this: