Hi,
Hopefully not getting too far off track but as noted by others it appears that the Finnish Airforce continued to use their B239s straight through to the end of the Continuation War with the Soviet Union (25 June 1941 – 19 September 1944 (3 years, 2 months, 3 weeks and 4 days)) [See Wikipedia].
As for the Bf109s, it is my understanding that they were not purchased until early 1943, with the first batch of 14 being delivered on March 14th of that year, and another 16 delivered on May 10th with that types first successful combat in the Finnish Airforce occurring on March 24th [see Link].
The link above notes some combined operations with both Finnish B239s and Bf109s such as an event on 21 May that appears to have included 11 Finnish Bf109s, 12 German flown Bf109s and 16 B239s. As such it does not appear that the Bf109 "replaced" the B239 in Finnish service but rather started to become their top fighter with others, including the B239, continuing to support them.
Specifically the link above also notes that during the Soviet's Summer offensive of 1944:
"During the Soviet offensive, which lasted 38 days, The Finnish Bf-109s and B-239s claimed 425 Soviet aircraft destroyed and another 78 damaged, while the Fw-190s of II/JG 54 led by Major Erich Rudorffer scored a further 126 victories."
Regards
Pat
Some small corrections, the Continuation War ended on 4 Sept 44
the first batch of 109Gs were 16 factory-new 109G-2s, the second 14 were second-hand but completely overhauled 109G-2s, some had been so badly damaged that they were in practice rebuilt planes. Later we got replacement G-2s for the lost ones via Luftpark Pori and still later more from Germany which were mostly sub-type G-6s for replacement of losses and re-equiptment for new units. Altogether we got 159 109Gs.
Finns used survived B239s also against Germans during the early part of the Lapland War in late 1944