dear iskhan,
welcome to Pak Bonsai.
yes this forum is to share the knowledge and know the alternatives for bonsai soil materials tools tree and pots.As you have asked about Ajwa date tree so it is possible to train it as bonsai.but it will be a tough job,for this you have to spend lot of time to learn and ask the friends.unfortunately there are few in pakistan who can assists you.but what we can,share our ideas as we are also new in this hobby.
any way plant your Ajwa in square pot instead of round,it will look good.
as you have asked about soil,
alternatives we can use are as below,
grit==== gravel"BAJRI"( we use it in construction,please chose small size gravel)
akadama/kanuma========brick shreds, take a new brick,break it into small size pieces or find some pumice and use it.
please dont use blocks as they are made from concrete in karachi use brick made by clay in "BHATTA KHUSHT"
after this mix some thick size sand and compost in it.
as dates dont like too much water and you have high level of humidity in Karachi i will chose the ratio as under
brick shred 40 %
gravel 15%
thick sand 10 %
compost 35 %
mix them well and use as soil.these are my suggestions according to my knowledge you can use better with ideas of other members.
for further on soil please read
https://pakbonsai.forumotion.com/bonsai-soil-f3/how-to-make-bonsai-soil-t41.htm?sid=51ea663ca3a18fd0d114daabe6ef22a0