You can use bitaddress.org, the "wallet details" tab lets you input a private key and it will generate a QR code.
Of course, to ensure more security, you can save the website to disk and disconnect the machine from the internet (or better yet, copy the saved page to an offline machine) before you input your private key.
I already have a vanity address and a priv key, so I would like to convert that.
Yes, you can do that with bitaddress.org. It does more than generate keys. Open the page, go to the "Wallet details" tab, input your private key and it will make the QR codes.