Love and Lavender has several free downloadable invitation suit templates. Many of them have a vintage feel (depending on what era you prefer). The Silhouette has a Regency or Victorian look. The Vintage Keys could complement many eras. Some of the downloads are specifically save the dates, or can be used as save the dates.
Feeling particularly crafty? Just download some free fonts and make your own template. DaFont has several pages of fonts that look like calligraphy, as well as pages and pages of Medieval fonts and Retro fonts. There are also plenty of other kinds on fonts to choose from on their page (see the menu at the top of the page).
Next up: Free Save the Dates
Following: Vintage Labels for Invitation & Save the Date Envelopes