I use Jason Naturals mineral sunblock on my little ones (used it on my son when he was a BABY last year). I also like California Baby & Albee (I think that's what it is).
I just go to my local health food store to get them most of the time, but you can get them @ Giant & Wegmans in the natural foods sections.
At the risk of this sounding like a sales pitch---with a baby that young, he really shouldn't be out in the sun at all & sunscreens can be ineffective prior to 6 mos. Using something like a Solarveil sling to carry him in, along with a wide-brimmed hat would be much safer & more effective. Solarveil has an SPF raing of 70+!!!!
I do have them available on my site (which is below if you're interested) & I do offer Mamasource members 15% off w/ coupon code "mamasource". Just FYI!
Hope that helps!
A.
www.ThingaMaSling.com