Hey Gary,
I am not aware of a good quality filtration system made for smaller ponds. Notice I said good quality, there are lots of lousy ones. I normally make my own for the smaller ones. What I like to do is take a large planter made out of plastic and turn it into a biological filter. It must be a square one so you can install bulk heads in it. I have made wet/dry type filters and flow thru type filters out of these containers. I use lava chips made for land scape for media. It sounds cheesy but for the drain coming out of the filter, I use a 1" bulk head. Then I take one of those cheepie Tiki torched and cut the bottom of it off and use it to cover the bulk head and be the drain putting the water back into the pond. It will look like a bamboo pipe coming out of the container adding water back to the pond. Put a water loving plant in the top of the container and it won't look like a filter any more.
As per a pump, I don't have any great ideas. Any submersible pump will work fine if sized correctly but a great dirt trap before the pump is a must. This is where the problems start. If the pump and dirt trap are in the pond, you will be getting in the pond every few days cleaning out the dirt trap, a major pain!!! If you don't mind cleaning the pre filter, it works fine but it is inconvenient. If you get a mag drive, supreme makes a pond pre filter box that attaches to the pump with no modifications. It works well but you must clean it regularly.
Plumbing a modest size UV will kill suspended algae too.
I prefer outside skimmer boxes with dedicated waterfall chambers that are also the biological filter. With an outside skimmer box, the pump is not in the pond and is protected from debris and much easier to service. The skimmer boxes have nets to trap fish, leaves and other debris with a thick filter pad below to trap the finer debris. THis type of set up is expensive, the smallest waterfall / bio filter box is over $200.00 and the smallest skimmer box is about the same price range. It's hard for me to suggest that type set up on a smaller pond, they work great but are pricey.
If you want an hand with a DIY filter, I'm happy to give a hand. I think I have a small one at the shop you could look at for some ideas if you'd like.