I have managed to secure some used R10 inlet valves which can be machined down for use in an R4 engine. Not the ideal but it is supposed to work.
I would prefer to have the real R4 Inlet valves.
Already contacted George (Whitehouse Motors) and he advised to look elsewhere as the Reno parts price came close to 95 pounds for four...
An R4 supplier in Germany (listed on your web page) has the R4 inlet valves listed. Unfortunately I have had no response via e-mail.
It is a question of lead time.. parts suppliers in Australia are advising 3 months before next delivery.
Paul