That information is not publicly available as far as I know.
Many years ago, Google did have a chart showing how many advertisers they had. That was maybe 2005 or so. I do recall the last couple of years were projections and something like 250k in 2007. I’ve heard estimates of 2 million today and that might be low, others say maybe 5 million. Based on a project I’m working on, my best guesstimate right now is over 2 million. I have nothing segmented by country. Bing would be less and a good guess would be 500k, possibly a million.
The way I would use this admittedly very rough estimate of 2-5 million in the world, based on population size, Hong Kong companies may be 2k to 5k Google Ads users and maybe 500 to 1000 Bing Ads users.