Naturally sales will have declined from when it was introduced. But on the other hand I would imagine sales are higher now than they were four or five years ago after a lot of Leica users went over to the M8 then M9. The mild resurgence of interest in film, it becoming a cult in itself, has meant that Leica sales for the MP will have risen again in recent years, along with other new film cameras, such as Holga's and Lomo's. Both high and low ends of the market are served for new film camera's by niche suppliers, so whatever sales there are will be reasonably strong pro rata.
You still have the dedicated amateur buying the MP, perhaps as something he has always promised himself, or just his next camera. Then you have the MP's bought because one has been seen on the shoulder of a Hollywood star, possibly just as a fashion accessory, but I'm sure some are used. And then you have the emerging markets, whether an MP is bought by a Russian oligarch or a Chinese industrialist there is an even bigger trickle down to the new middle classes.
So selling 2 or 3 isn't a very realistic figure for even a 'I hate Leica' person to guess at, but possibly more like wishful thinking. I would have put it in the 50's, or 60's, maybe many more, worldwide, week in week out, not accounting for Christmas. After all, and who'd have thought it, makers of high end, hand made Swiss watches are having their best years ever right now, after those panic stories about markets being flooded with cheap imports and people not needing them because they have a mobile phone.
Don't underestimate Leica because you can't imagine how many MP's they sell, you might do better by imagining the unimaginable and you'd be much closer.