Ask any gathering of session musicians about what tune is what and how they should be categorised and you can settle down for a good long and possibly heated discussion. One persons hornpipe is another ones schottische. What started off as a mid 18th century country dance ends up as fast Shetland Reel. Tunes morph, change tempo, split and recombine in different ways, change title, emigrate to another country and style... and so it goes on.
Folkopedia is not destined to contain a definitive collection of tunes but it can provide a route to many different collections and an opportunity to find some of the research undertaken over the years.
Here are some websites from where webcrawlers search the internet for you for tunes, often in ABC notation. They all cover basically the same ground, but present the results in slightly different ways, so choose the format you like best and remember that you may find a missing tune by choosing a different engine if your first choice doesn't find it. All you will need are a title, or a section of the tune in ABC notation.
Behind these links you'll possibly find titles, history, links to abc code or some actual code, maybe MIDI, links to associated dances or songs........