The Main Switch

It is possible to use your main breaker panel as a power disconnect switch, but those are not meant for daily use. The main switch on your kiln should be at arm's length. It is a kill switch in case anything goes wrong. I can't say I've ever needed one but it is there if I do. I find my power disconnect switches usually at the Big Box Stores. If you want something more expensive go to your local electrical supplier. This can also be bought online. What you are looking for is a Double Pole Single Throw (DPST) 240VAC Switch. These can be with fusing or without, but the point is to mate it to the needs of the kiln using the 85% rule already discussed.
Shop around for this item. Old is not bad! Look in some of the old hardware stores. I use the boxes with a pull arm on some of my favorite kilns, just make sure the rating is up to your needs. This can be a great yard sale item.