Check with local independent garden centers to see what they have. My very rural garden center makes up a special compost/topsoil mix for filling raised beds, and they deliver.

Just in case you didn't know there is a Soil & Compost forum here.

If you compost then adding it to your soil is the way to go or you can probably purchase bagged/bulk compost somewhere locally.

If you are looking for a commercial bagged additive then it would all depend on how much you need and what is available to you locally. Shoot even Walmart here carries bags of composted manure and humus if you can't find something else.

Dave

I have 9 raised beds. Adding soil is a yearly, sometimes twice yearly event. As Dave said, there are bags of composted manure which do pretty well, are fairly inexpensive, and are easy to manage without a truck (or a willing husband). I keep a few bags on hand all the time.
If you don't have a compost pile, start one. Homemade compost is the cadillac of all soil amendments and couldn't be easier to make. Of course, that doesn't help you today, but if you get started, it will be an enormous help later on.
If you can find it, aged horse or cow manure is much better than the bagged stuff. We have horse stables at our Ag Center here and I have been able to sweet talk friends with trucks into bringing me a load now and then. (I do free garden designs for them in exchange. Maybe you have something to barter?)
And then, there is the wonderful world of cover crops. This is my first experience this year, but I sowed red clover in my beds last fall, let them grow through the winter, and then turned them in just as they began to flower. I am excited to see what effect they have, but I was impressed with how easy the turning process was. If they live up to their advertising, this will definitely become an annual affair. The seed was incredibly cheap and I just threw it onto the beds after I did my fall clean up.