Due to the position of the shoulder on the center pin, it may be difficult to find the correct one for your dash 3. The new ones I've ordered recently don't have the right length at the rear, where the pin interfaces with the breechface.
An alternative to finding and fitting a new pin is to carefully remove the excess material that has been peened out on the front edges of the existing pin. After cleaning up the end of the pin, figure out how much length is needed to make the pin interface with the locking bolt properly. When the thumbpiece is fully depressed, the front end of the center pin should extend forward to even with or just a bit forward (.005"-.010") of the end of the extractor rod.
If the pin is a bit short of reaching this desired length, you can shorten the end of the extractor rod a bit, and re-profile, or remove material from the extractor rod collar in the assembly. Removing material from the collar will make the entire extractor assembly, except the center pin, shorter when it is re-assembled. This will move the extractor rod back the desired amount, and correct the issue with the front locking bolt catching on the end of the extractor rod when the thumbpiece is fully forward. The collar can be easily shortened by laying it on a stone, and while holding it with the fingers, working the collared end back and forth on the stone surface.
Another possible and easy way of solving the problem that precludes the necessity of purchasing and fitting a new center pin.
Carter