I have an 3 OD solid aluminum round rod I need a large section drilled out, to where the wall is 3/16 in thicknessWhere do I go?

I'm not a machinist at all and all the local areas in the Los Angeles region appear to be industrial machinists, producing massive metal items for construction, etcThe rod length needs to be shortened to 2.5quot; from a 6quot; rod length I haveAm hoping to make a cyclinder washer to cover over my car oil filter (2.5quot; OD) and then have a heat sink go over that aluminum washerThe oil filter heatsinks on the market right now are all 3quot; OD and my car's oil filter is 2.5quot; ODThus the washer will fill the gapThank you.