I found several European dendrochronologies recently which might help with the gaps in the Roman AD period. None of them are recent, so you might already know about them:
1) There is a Polish one from 474 BC to AD 1141, but it has short 43 year overlap at AD 300 and relies on German chronologies at that point. M. Krapiec, 'Subfossil Oak Chronology (474 BC - AD 1529) from Southern Poland', in J. Dean et al (eds), Tree Rings, Environment and Humanity..., Arizona 1996, pp.813-9. P.816 gives block diagrams and t values but there is no annual data.
2) A Dutch BC chronology was described in the same volume (pp.769-778) but this led me to http://vkc.library.uu.nl/vkc/dendrochro ... terdam.pdf which is the published version of a PhD by Esther Jansma, RemembeRINGs..., (NAR 19), Amersfoort 1995. Chapter 5 covers chronologies from 325 BC to AD 563, one of which is apparently continuous over the whole period and another is said to cover AD 190-395. In Appendix C are the annual ring width indices for the chronologies (but not for individual trees).
3) The ring width indices for the North German bog oak chronology (again, not individual trees) were published in graphical form in H. Leuschner et al, 'Subfossil European bog oaks...', The Holocene 12:6 (2002), pp.695-706 (graph on p.699 - I have e-mailed a scan to Petra).
Do you know if any of these groups would be willing to release their full data for the relevant period?