Autopia is a great site indeed.
The Mother's clay bar is available at AutoZone and Pep Boys near me, so check into that.
Your rims situation reminds me of the tar and brake dust embedded rims I see all the time in my work, and there are a few approaches.
Safest approach; You can try a non-acid wheel cleaner, and add some polishing compound to a damp cotton rag to rub a bit after you spray the wheel cleaner. You will probably have to really work it. Rinse thoroughly. You can also try the clay bar. Break off a small piece of a new clay bar, and try it with some Dawn and water as a lubricant, and rub then rinse . Another thing to try; Go-Jo hand cleaner( the non-gritty kind) or that Permatex paste hand cleaner. It cleans extremely well and won't harm the wheel finish.
As a last resort, you can use a hydrofluoric acid wheel cleaner, the type intended for wire wheels (Bleeche White is also one of them ) BUT, be advised, while it will remove alot of that grime fast, it can/will often slightly (or greatly depending on how long you leave it on ) etch the finish in the wheel, making it more porous and even easier for dirt to bond. You MUST do one wheel at a time when wheel is COLD or you WILL ruin them in short order. Don't leave any acid wheel cleaner on a wheel for more than 1 or 2 minutes. Rinse very thoroughly.
There's a good chance there's some etching going on, so you MAY not be able to get it all. Wheels get pretty hot and bake stuff like brake dust and tar etc. in and start to eat through the clear on the oem wheels. Time is always the enemy in car care; some things just need to be attended to on a regular basis. Leave it too long and in some cases, you're screwed . This applies to wheels, bird bombs on paint, water spotting, stains on seats/carpet etc. Good luck, email me if you need further help.
onequiksc@cfl.rr.com
Dan Holleran
"Automotive International Bronze Level Trusted Detailer"
www.autoint.com