Gold is denominated in U.S. dollars so one of the regular gold ETFs could work. PERM uses the ETF Securities Gold Trust (SGOL).
A similar portfolio can be constructed for Canada using the iShares MSCI Canada Index Fund (EWC) and Index IQ Canada Small Cap ETF (CNDA) for equities, the Rydex Currency Shares Canadian Dollar Trust (FXC) for the currency and the PIMCO Canada Bond Index Fund (CAD) although with an effective maturity of 13 years it is still shorter than the original Harry Browne idea.
And again with gold denominated in U.S. dollars SGOL can work, as could the SPDR Gold Trust (GLD).ETFs would also allow for a permanent portfolio for Germany and China and as more specialized foreign bond ETFs continue to proliferate there will be other choices like this. AUNZ, FXA client holdings