I cannot find any information on the milky spore product being "banned." However, there has always been a number of problems with relying on this product, and I think garden centers are FINALLY wising up that it does not produce the results that customers are hoping for. Some of the problems:

• Milky spore (Paenibacillus popilliae (formerly Bacillus popilliae)) ONLY kills the grubs of Japanese beetles.  It does not harm the grubs of any of the other beetle species that infest the average Midwestern lawn.  Since Japanese beetle (JB) grubs make up only a small percentage of the grubs in an average lawn, relying on milky spore will still result in grub damage to turfgrass.
• The bacteria that causes milky spore is a naturally occurring soil-borne bacteria.  According to the University of Kentucky, it can be found in almost all turfgrass areas, even those not treated with the commercial product.  Adding more product to the lawn does not measurably increase infection rate.
• Milky spore is a weak pathogen.  Even in treated lawns, only 15-20% of JB grubs show infection (Univ. of Kentucky).
• Milky spore is a living bacterial product.  I don't know if it still a problem, but back in the 1990s, it was discovered that because of packaging and shipping practices, most of the milky spore products contained only dead bacteria by the time consumers bought the product. 
• If you are trying to use milky spore to reduce JB adults in your garden, it doesn't work.  Even if you could magically kill 100% of the JB grubs in your yard, you will still suffer adult beetle damage, because adult JB can fly up to 2 miles in search of food.  You will get beetles from your neighbor's yard, and the yard across the street, and the yard in the next township over...

I hope this answers your question somewhat.  If you still wish to use milky spore, you can search for it on the internet and buy it mail-order.