Andrea; I looked around some online but couldn't find any 'custom grafting' to that extent. A few Nurseries will 'make a tree' for you, but one variety only...
My first suggestion is to 'do it yourself.' Buy the base varietys you desire, then graft on the second variety to each tree. You could either dormant graft, or 'bud' it next summer. The Home Orchard Society
gives classes on each.
Second suggestion: you procure the base variety trees you desire, both pear & apple. Bring them (potted or root wrapped) to the HOS "Fruit & Berry Cutting (Scion) Exchange"
this spring and pay ($3 or $4?) to have one of 'us' dormant graft your additional varieties. If I make it in to graft (my 8th or 9th year of bench-grafting @ HOS), I'm willing (for their small fee) to put on as many varieties as you have limbs. Any of us could do it, I think - and if it looked really challenging
- they'd send you to me anyway ... while they sit & grin.
I have several trees done this way. I'd bought a Northern Spy
for example, then grafted on a Ribston Pippin
to one of it's young limbs. Keep in mind, the tree will need limbs; if you mail-order it, make sure it's 'branched and un-pruned.' So, you could do it - or we could do it. If you bring them into our Spring Event, there will be many free dormant 'cuttings' (scions) of apples and a whole lotta pear varieties to choose from. Just do us one big favor - decide on your varieties before you come to have them grafted! It's daunting to choose "A good one" for our clients...
That said; you should probably look over the following discussion on multi-grafted trees: viewtopic.php?t=40
I don't know if you desire two varieties for pollination, or choice..? If it's for pollination, do your homework! If it's for 'choice,' ...consider pollination...