Can an urn be personalized if it is bought online?

My husband & I have sadly decided to put our very old & frail family dog to sleep. My young children are devastated with the news. We promised them that they would be able to leave their own messages for our dog & have them engraved on the urn for his ashes when he is cremated. As we live in a small town, no one here is able to custom make it for us. We were then wondering if this engraving would be possible if we ordered an urn online. Can anyone help us with this? Thanks in advance!