Sydngoose brings up several good points. Just by your question of....."Does Parker sell them?" I'm guessing this is something you have VERY limited knowledge of and with that....Zero experience doing?
It would not scare me one bit.....But it's still expensive, as I have done them in the past.
You don't contact Parker for a Bracket.....Parker get's them from Armstrong. They use to get them from Stainless Marine.....Note that stainless Marine is a manafacture and builds a LOT of stuff in Stainless....BUT....Brackets are built of alum. 5052 series alum is used......There are other manufactures that are not well known.....Such as D&D marine...He has the best online info about mounting the bracket. The guy has a website and sells them.....They are actually built in a backyard shop that he farms out to.... There are a lot of things to it. I use a piece of 4in U channel on the inside of the transom as a backer.....Not sheered square plates. Those put point load stress on the transom. Yes....you see that used.
Along the U channel on the flanges.....not the face I drill 3/16in holes every 6in .....1/4in in from the edge.....The outboard ends are radiused, so no point loading out there.....The holes are installed for tye wraps to go thru latter on while rigging the boat and tying things up neatly.
Swim platform..... You want it to come to within 2in of the outside edge of the transom....Not be flush with it. It looks better and helps protect the bracket. If you buy a in stock bracket.....It will be short, as it's probelly made for a boat with a 8 1/2ft beam....and the Parker has a 9 1/2ft beam....[Not the actual measurement of the swim platform.] Size of the tub.....How big / wide does the tub need to be to help support the engine at rest? Remember....The whole volume of the tub....doesn't come into play.....It's Only the part in the water. Parkers get away with a smaller tub due to their Fat Ass..9 1/2ft beam.....They have a wider transom supporting more flotation......Still on a single engine....I'd shoot for a 30in wide tub.
Ok...Thats enough......I;m tired of typing.