As JK2 states, it's extremely unlikely that you'll find an online service which puts an 'instant package' together for you. The travel operators who offer this type of service for European destinations are able to do so because European travel usually only involves a single flight. Things get far more complicated when you need to take several flights, with different airlines.
I suggest forgetting about the web altogether (apart, possibly, from checking for reviews of any hotels which are suggested to you). Try to find a well-established, local independent travel agency. (Avoid the big High Street chains ). You really need to speak, in person, to somebody who really knows their job.
Be wary of anyone who tries to route you with eastbound travel (which is probably what some of the inexperienced staff in the High Street chains would do). The best route is probably westbound via Los Angeles. Aer Lingus fly from Glasgow to LA, with a change at Dublin, twice a week. BA fly the route, with a change at Heathrow, daily. Flight times vary between 12 and 16 hours, depending upon connections. Then you've got to wait for a connection for an 8 hour flight from LA, possibly with Air Tahiti Nui.
Chris