Normally the thai fares to KTM are more expensive than others. I would look into flying into Delhi on either swiss, air canada or Lufthansa and take a jet airways, or Indian arilines (now air india) flight from there to Nepal, and use the savings to fly some fligths domestically in Canada to get the miles.

Keep in mind some of the lower fares especially on Singapore airlines and a few on thai do not allow full mileage accumulation.

For fares to Delhi look into India specific websites such as www.yatra.com or www.makemytrip.com