I'm looking for a new DT2 piston, 0.50  oversize.  I know I can get forged pistons from Wisco and Wossner, but I'm after the cast ones.

Not a fan of the extra weight of the forged jobs.

I'm located in Australia, and when some come up on Ebay, the postage is always astronomical.

Any one out there know of aftermarket cast pistons or have an original DT2 70.50mm piston they would like to sell off?

Contact Enduronut.

Also you might want to correct/clarify your post... you seem to be asking for a 70.75 mm and then a 70.50 mm...

(Forged normally only come in steps of about 0.50 mm)

Apologies, all fixed, should be 70.50.

Aren’t Wossner pistons lightened? If the extra weight of a forged piston is your concern, maybe write off buying a Wiseco but give Wossner a second look? Just curious, I ordered a Wossner for an upcoming engine build and had the same apprehension about buying forged modern pistons but was told they were lightened and some of the better pistons money can get you. I could be wrong, would love to hear more

I've never noticed a Wiseco or Wossner to be appreciably heavier than stock. It takes a lot more machining to lighten a forged piston but both manufacturers seem to do just that. 

If you just ordered one, maybe do a weight comparison against the stock one on a postal scale? 

I might have a couple of old ones around I could compare. 

I put a Wossner in my DT2, have no issues and bike runs great! I liked that they coated the skirts vs them being bare aluminum.

If cast pistons are available, they are always to be preferred for use in 2T engines. Cost is also lower, which is pretty useful. 

Cast pistons, use closer bore clearances, and are lighter. Forged pistons are good for 4T motors being used in turbocharged or supercharged form.

Back in the days of GP500 racing, all manufacturers used cast pistons, except for Kawasaki, who used forged pistons for one season, before reverting to cast the next year.

The DT250MX uses a 70mm piston. Have a look at the Mitaka website, which will provide details of that piston, which hopefully might fit your bike?

I used a Namura teflon coated piston in one of my RMX250's. Beautiful piston kit but can't find one for older Yamy's like yours.

Cast pistons are no longer made for old bikes, but it's very easy to have a look at the Mitaka site, and see if a piston intended for a newer bike will fit.

The truth is there are plenty of new high quality cast pistons available for old bikes and some are still made today.  Depends on what you're working on. 

(Not all cast pistons are created equal.  Some of the cheap brands that have flooded the market fail nearly instantly causing major damage.)

Nothing wrong with forged either if what's you can get. 

As far as looking in a catalog finding a piston from a different bike of the same size, pin height, etc. that will fit, it's critical on a two stroke to make sure the rings are pinned in the correct (or at least acceptable) positions.  Catalogs often don't identify ring pin locations.  And details matter in real life. 

Also there is still a decent supply of NOS pistons out there for many models.  Member Enduronut has helped out quite a few members who needed pistons and rings, he's also quite the expert on which piston can be substituted where and navigating the quagmire of Yamaha part number supersessions.