The U.S. Chamber of Commerce often says it speaks for 3 million members, businesses both large and small. What it doesn't promote as readily is that 19 supporters last year provided a third of the trade group's total revenue. Documents filed with the Internal Revenue Service this month show the chamber drew its 2008 funding heavily from a small group of contributors, with each paying more than $1 million. Within that set, some gave very large sums. One company or person provided the chamber with $15.3 million last year, an amount more than 10 percent of the influence group's $147 million revenues. Another gave $8.2 million, and a third $2.9 million.