I agree with Desota - I would be quite surprised if you could get an R-class share outside of an employer-sponsored
retirement plan.
When American Funds came out with class F shares (now called F-1), they were available not only through advisors, but through some offbeat discount brokers (e.g. Citicorp Investment Services - doesn't exist any more). Later, when American Funds added F-2 (same as F-1 but w/o 12b-1 fee), they seemed to tighten up on access to the F-1 shares.
Nevertheless, there appear to be a few access points remaining. I don't know how useful any of this will be, but here's what I know about those access points.
Several HSA (Health Savings Accounts) offer access to a limited number of mutual funds (i.e. they have a menu, like an employer's 401(k) plan does). Among these offerings one can often find one or two American Funds (class F-1). For example, here's the
fund list from HSA Bank.
Some HSAs offer brokerage options, and these tend to be treated as
retirement accounts or institutional accounts, rather than generic retail accounts. As such, they seem to offer greater access to some investments. Many of these HSA accounts use TDAmeritrade as the brokerage partner, and it looks like AMPFX (AMCAP F-1) may be available that way, NTF, despite a search on the brokerage site turning up a page saying the fund is not available for sale there.
Another back door is via a no load VA. What you get there are usually clones of the retail funds, but that's often close enough. You can access the
American Funds Insurance Series VA funds through
Jefferson National Monument Advisor VA. There isn't a clone for AMCAP, but there is one for Growth Fund of America.
Finally, there's the solution for the high rollers - dump $1M into American Funds, and you can get their A shares without a load. (Though there's a 1% redemption fee if you sell within a year.) If you're investing that much, you're probably not worrying about whether there's a transaction fee.