DancingMommy said:
Now if I want to MAKE a tailsuit, where might I find a pattern for such an animal???
You have to make the pattern yourself.
You'd want to start with something for a tailcoat of some sort - either a commercial pattern, something derived from an existing jacket, or using the old (buggy) drafting instructions from the
Cutters Practical Guide (costumes.org). You'll want to shorten the torso a bit above the natural waistline to give the long-legs look of standard dancing. Don't try to wing it from a tuxedo, suit jacket, etc pattern as those are completely different - you need something with the proportions and panel division of a tailcoat as a starting point.
You'd make a fairly firm canvas muslin of the torso portion of the jacket without sleeves or skirts (tails) and get that to fit right. Put some stiffeners in the shoulders - the acrylic "felt" sold for kids craft projects seems to work well and shapes with steam. Then you'd make another with the arm holes too small, and cut them just barely big enough to allow the suitable range of motion without distorting the body of the canvas (ie, you want the fabric to go much higher under the arm than normal). Take a normal over/under sleeve pattern and flatten the cap quite a bit - primarily you want the underarm side to fit in dance position, but you need just enough extra fabric on the top and back so you can drop your arms between dances. Make a test sleeve in wool and attach it to the canvas, easing it in as in social tailoring, but without a shoulder pad or sleeve head.
The skirts on a dance tailcoat are longer than in social tailoring, and they may need to be cut a little differently - an existing set of dance tails in a similar size is the best guide. They will need some sort of weights too.
You'd have to make some decisions about how you want to interface the final product - usually gentleman's jackets are interfaced only on the front, while ladies are front and back, but for dancing you might want to do the back as well. If this should continue into the skirts is an open question...
In some ways, the hardest part is general fitting, putting everything together neatly, especialy around the lapels (they MUST be peaked, not notched - suprisingly several big name dance tailors usually do this wrong). This is the kind of area where a good social tailor experimenting with a something new like dance tails would really be able to make use of his skills, compared to an amateur.
The trousers are a bit simpler... waistline will need to be extended up to match the higher cut of the jacket in front, and they should be set up for functional suspenders. It's probably worth lining the front to the knee, and foot loops or cuff weights aren't out of the question. Don't even think about pockets (well, at least no front or side pockets - you could get away with a back pocket, or internal convenience pockets in the jacket, but they have to be empty when actually dancing)