In the entire series of Harry Potter, we have met European wizards utilizing Wands which have never been mentioned to have more than one wand woods, either in blended or different parts made of different wood form.
However, the wand is a complex tool and there do exist Wizards and Witches who have gone past what Ollivander considered inconvenient or dangerous. For instance, Salazar Slytherin made his own Wand out of Snakewood and Basilisk Horn.
Thus, while Ollivander might not do it, there might exist some other wandmakers or people who have crafted wand with parts made from two different woods.
Rowling took inspiration for wand woods from the Celtic Tree Calendar
Celtic Tree Calendar
- Birch (Beth) December 24 to January 20
- Rowan (Luis) January 21 to February 17
- Ash (Nion) February 18 to March 17
- Alder (Fearn) March 18 to April 14
- Willow (Saille) April 15 to May 12
- Hawthorn (Uath) May 13 to June 9
- Oak (Duir) June 10 to July 7
- Holly (Tinne) July 8 to August 4
- Hazel (Coll) August 5 to September 1
- Vine (Muin) September 2 to September 29
- Ivy (Gort) September 30 to October 27
- Reed (Ngetal) October 28 to November 24
- Elder (Ruis) November 25 to December 22
December 23 is not ruled by any tree for it is the traditional day of the proverbial "Year and a Day" in the earliest courts of law. (Celtic Name)
Closer analysis and cross comparison with Pottermore reveals that some wand woods like Elder and Rowan share similar affinity traits and we can see that they are separated by only one month.
Thus it might be possible to pair the two. Wands with similar affinity can be paired together.