Just Jap and others sell HKS 'replica' wastegates. The JJR is the same to lookat and in dimensions as the HKS 40mm standard wastegate. The price of a new HKS is $750, the JJR around $270. I didn't buy one [found a s/h HKS that needs a new diaphragm], but everyone that I had contact with that had a replica reckoned they were OK. I think its a bit of a gamble, but if Just Jap sell them [and stand by the product] then they must be value for money.
PS I notice that other companies sell them as well, I just used JJ as an example.