Airtours/MyTravel then Thomas Cook all operated Las Vegas non stop on Boeing 767-300 aircraft. I even think Leisure Intl/Air 2000 did the same.
Although im not sure if LAS would be a viable route for LS as TCX operate from MAN, then you have CO, US, DL, AA with one change, and also BA start there LHR service this month which i think is daily, along with VS from LGW again Daily.
My money would be on SFB initialy.