Where are all the mixtapes?

They're still there.
New Hip Hop Mixtapes every day.

Only I don't have the time to monitor for new ones at present (and in fact I haven't since the middle of may) and to be very honest, I'm hardly listening to any Hip Hop music at the moment.
I find myself doing this every so often; not following the music and not following the culture.   I still love it and I'm certain I always will, but sometimes it just the same old shit and I'm tired of it and I don't feel the need to expend any energy until I can see that the effort will be rewarded with some quality tunes.
So roll on Detox Mr. Dre; Mr. NWA; Mr. AK - coming straight out of Compton y'all better make way!
We need the Chronic Part Two too.  Go get it from the Old Dude with the mechanical legs.

Back to the point.  The website that used to be, in my humble opinion, an excellent one to visit if you were unable to determine which Hip Hop Mixtapes on any given online mixtape store were the most recently released has now gone.  If you wanted to know what Hip Hop Mixtapes were released today, or yesterday, or on any given day between 29th December 2003 and 18th May 2005 then you could have done worse than to have a look there, but now you cannot.
The pages there are currently redirecting to their respective pages in another place, but before February is through it will no longer do that and an archive of the pages at www.jahboite.co.uk/mixtapes will be all that remains.
It's a shame because it was a useful website.  I tend towards thinking that I may have cruelly cut it off at it's source just as it seemed to have mastered walking and was beginning to break into a bit of a run.

Who knows what may happen though, in the future.