I agree -- there's nothing wrong with mismatched china (or crystal or flatware). If you're choosing chargers, maybe choose simple ones, especially if the china is a more elaborate pattern.
When we have a very large group, especially at holidays, we have to use two or more patterns. If there is more than one table, sometimes I put one pattern on each. But sometimes I alternate patterns, sometimes I just put them wherever, and sometimes I even mix pieces at each place, if I like the way the patterns look together, or if I'm stretching with glass dishes. Even if you think it looks funny when you first put down the plates, if you can't make it come out even or something, don't worry -- when you put all the other things on the table, like centerpieces, salt and pepper, water pitcher, etc., it won't even really be noticeable.
Replacements.com is usually so expensive. Sometimes eBay sellers have things.
I agree that matching isn't always best. I'm not crazy about serving pieces that match the china or flatware, for example, sort of like a hotel or restaurant, and the other ones you have are usually more interesting. Besides, even if you do have a few matching serving pieces, you're probably going to have to use a few non-matching ones as well anyway. I have a few serving pieces that match my silverware and I often choose to use others instead just to mix it up.