I researched developing B&W slides earlier this year and experimented finding a formula and chemicals I could get hold of but don't have facilities at the moment. Some of the chemicals I had to get fron eBay suppliers. There are a ton of threads on this site and others that give a lot of practical information and experience on the process, just use the search facility.
The Foma kit is available here but is produced for the Foma R100 film and you would have to do trials if you wanted to use other films. I noticed recently that AG Photographic appear to have priced the Foma kit at nearly double its usual price but Silverprint had it listed at around £30 something the last time I looked. I am guessing AGs pricing is a mistake. Either way it works out quite expensive.
Others here have mentioned dr5 but I could recommend Photostudio13 in Germany who process a number of mainly Rollei marketed films. They are cheaper, the service and quality is very good and more convenient for UK based users.