Marhaba....keefalakh Hisham.
I'm in Riyadh and we have one Airfix/Humbrol supplier but stocks are inconsistent so I sometimes I have to seek alternatives too.
Turps or Turpintine substitute are OK for thinning enamels and cleaning brushes.
Also ladies nail boards are good substitutes for sanding sticks. They have two sides, one side medium and the other fine. They are a lot cheaper too.
And for filler you can mix styrene cement or superglue and talcum powder to a paste.
If you have an Art materials shop, you might find matt fixative used for sealing pastels and charcoal sketches. This may be a substitute for dull-coat or Humbrol matt varnish. Maybe someone can verify this.
Good luck
Cheers
Peter