@ the Sage,
The directives on preferential treatment are rarely enforced (just like very many other clauses in the PPD Act. To be honest, it is unlikely that you'll given business on the basis of these "preference" clauses.
As I said in the earlier post, your best bet is to get involved in as many procurement processes as possible. As a target,make sure you are prequalified as a supplier in as many public bodies as possible (say at least 10). This is going to cost you some money (each entity may require anything between 2k and 5k for purchase of prequalification documents). My advise is avoid the bigger agencies for now (the KRAs, the KPAs, bigger ministries, etc). Target the smaller parastatals and smaller ministries (ERC, TARDA, KLB, ministry of Northern region, local authorities etc). There's less competition there and the bureaucracy is not that convoluted.
It is hard work and requires frequent follow ups and basically keeping your ear to the ground. And remember, government is the largest consumer everywhere in the world. If you are not doing business with the government, you are missing out on a sizeable chunk of the market.