Hi Don, I'm using FS2004 and I too have a couple of 'addon' airports missing from the list of airports visited on this years 2015 World Flight.
One airport (KTUP Tupelo) I have to use just an AFCAD file. The rest I've either bought from the payware sites or located on the freeware sites. The freeware sceneries are remarkably well designed!
I don't know if this is any help to you, but there is FSX payware and freeware scenery available for the airports you have listed: VTBS. OTHH. SEQM.
and go to File Library/search files. file section is 'FSX scenery' and type in SEQM in the 'search for text'.
You should have two files that you might want to download: FSX Scenery - North Central Ecuador v2 - and - FSX Scenery--Mariscal Sucre International Airport. There is also a freeware south central Ecuador scenery available too.
has FSX Sceneries for both VTBS and OTHH or alternately there are two VTBS freeware sceneries at the flightsim.com website. There isn't any freeware FSX SEQM scenery at that site yet!
You may have already sourced these sites, but since you posted your information I thought I could be of help.
Hope you enjoy World Flight 2015 like I have every year since its inception.
Regards, Ian Ellis.