What is a "large" Oak? Diameter of stem is likely to dictate the size of saw you might need.
If you are fond of Jonsereds- about the earliest starting point might be 600 series saws- 630 being the older and very similar to a Husqvarna 162 but a bit more refined, then the 670 while being that bit gruntier and similar to perhaps a 268XP is its own beast and heavier than the 630- but not by a whole lot, then the 625- which is pretty much a red and black Husqvarna 61.
Or into the 20## saws- like the 2065 and 2070- similar to the original Husqvarna 365 and 371, then onto the 21## - like the 2171 or down to the 2152 if 50cc will do what you need?
The 21## and later Jonsereds are most like their Husqvarna cousins and parts are more easily found.