You might not like this, but Rangers have a huge following both domestically and internationally.
They have a 50,000 seated stadium & even in Scottish Division 3 the home average attendance was over 40,000.
That's up there with the biggest clubs in England in terms of average attendance - and they could probably fill a bigger stadium regularly.
The key though is the broadcast markets. Because the Scottish league is so shite it hardly ever gets picked up by overseas, or if it does, it's for a pittance.
Rangers, like Celtic have one of the most developed network over overseas supporters clubs.
Last year they developed Rangers TV as an on-line broadcaster very successfully - streaming all games live.
Their plan has centered around developing this medium to capture significant direct revenue streams.