I was poking around the internet about a month ago looking for the same thing. One interesting thing I found was a computer program that you could set up to forecast weather for your exact location (including barometric pressure). It sells for about $200 bucks though and requires a bit of footwork in order to customize it to your location. Dust off those climatology books! http://www.wxsim.com/
If you want to convert millibars to inches of mercury (inHG) multiply the reading in millibars x .0295
Your best bet is buying an Anglers Edge to keep on hand. Its about the size of a handheld GPS unit and runs on a few batteries. It identifies other peak feeding times as well. Bob Mehsikomer swears by it. You can buy them new for under $100.
I've been a pressure watcher for a while now and there's just no easy way to get it.
I had an Angler's Edge for a while and it's really a pain in the butt... each location you fish at needs to be entered by longitude and latitude, most of the time in a format different from that in a GPS (decimal degrees vs deg/min/sec). It's good from the standpoint that it gives you a specific number for a location, but at the same time, my time on the water is fishing and not messing around with something to determine the best time to be there. The thing doesn't have an off button and would miraculously turn on when it felt there was a change coming...even in the middle of the night, so I had to remove the batteries between uses.
It's just something that is tough to judge, you can't always feel a change in pressure, it's not uniform across a system, so just because the thing detects a change, it doesn't mean the fish are scarfing up bait.
I now subscribe to the K.I.S.S. method of covering more water increases your chances of contacting fish and being proficient at the basics(casting, hooking, and fighting fish) will put more fish in the boat no matter what the conditions.
Unless you found a site that would give you pressure in your specific area, it's increasingly worthless the farther away you get.
I have the Angler's Edge and stopped messing with it for the reasons stated above. The main reason I wanted to find a site that listed specific baro-pressure, was to attempt to draw correlations between active fish days and the local barometer AFTER the fishing day is over.
For the past several years I have been paying specific attention to the time of day we move/catch fish and I am not noticing a huge correlation between fish movements and lunar charts but I have noticed a strong correlation between local weather and fish activity. (Keep in mind that 90 percent of my musky fishing is on a river, not a lake.)
I fish when I can and rarely ever plan my 'fun fishing' around those types of variables like I used to.....well, except during the summer months when I have a little more flexibility in my schedule.
I was just trying to find a site for current baro-pressure so I could see first hand the effects of baro on fish activity.
Put in the zip code and then on the left side of the screen you will see a box with current conditions. There will also be link in that box toward the bottom of the box that says "Weather History for This Location". Press this and you will be able to search by date. The search results include a graphical plot of the barometeric pressure. It appears that the results provided by zip code are set to find the nearest airport AWOS.