I am looking for the same information, so look forward to your replies. However I bought my visa for Mauritania at the border when entering from Morroco last year, so I am hoping to be able to do the same again from Mali. I understand that it takes two days at the embassy in Bamako.
I am driving a Defender 110 300 Tdi up from Mali myself, and hoping to be in Mauritania around mid July. If you are goingup do you fancy driving up together, perhaps doing the Tidjika to Atar route?
Hope to hear from you,