There is no reason to add pseudoephedrine to any type of salt or mineral block associated with the feeding of bovines. AFAIK Pseudoephedrine is not approved for use in bovines, ovines, porcines, or equines, therefore it would be illegal under USDA/FDA regulations to add pseudoephedrine to a salt block (at least for slaughter cattle, which have stringent drug hold requirements). I could be mistaken, however I doubt it...
Now let's think about dosage. Medicated blocks are designed to deliver small amounts of medication to the animal. On average, (from what I remember) ~100mg of active ingredient per head per day is a target, (depending on the active of course). Remember these blocks are designed to deliver trace amounts of medication to the animal. Therefore the pharmaceuticals supplied must be efficacious when supplied in trace amounts. Total consumption of block averages around 80g per day (depending on molasses content). An average bovine would need ~12g of pseudoephedrine in order to realize any therapeutic value. Large dosages such as this are not intended for mineral block administration. Therefore I feel very confident in proclaiming that there are no available mineral blocks on the market that have any pseudoephedrine added to it. It would not make any economic sense, and in the US it would be illegal AFAIK.
much_love
methyl_ethyl