I have an offset umbrella with a 't' metal base that used to have plastic end caps. The caps have disintegrated in the sun and I'm trying to find replacement caps but can't seem to find any place that carries them. Any idea where I could find some?

Try using Google... put as much information for the manufacturer and model number as you have... and you will find someone that has parts. You can find some very rare stuff that way. That's always one resource I use.

If you are in the US, Home Depot, Loews, or any DIY project store can offer you some creative ways to replace those plastic caps. Maybe with metal ones and some Gorilla Glue? Browsing through the stores may be fun too, and give you ideas if the manufacturer, or the store you bought the umbrella from is unavailable, or unhelpful.

Finding exact OEM parts like this is nearly impossible since most manufacturers do not stock part like this. Go to ACE or all big hardware store and look for things like http://www.essentracomponents.com/caps-plugs/push-fit-plugs/tube-inserts-glides?src=em&gclid=CI7z17ft2b0CFdBcMgodOFoAmg or Google plastic end caps to find a company like my link