Greetings from
Nebraska. I buy all of my specialty drill bits from McMaster Carr. I have had very good luck with them and usually receive my order in 3 days or less.
They offer a lot of options including Carbide and Titanium-Nitride coated Carbide. Solid Carbide is not cheap! A 7mm will cost in the neighborhood of $40-$50, but a carbide tipped bit will run around $20 or less.
This Link should take you to McMaster Carr's 7mm drill page.
Regards,
Dave
PS In my case I am not adept at sharpening drill bits nor do I have a sharpening machine or jig, so Carbide bits are my preference. Sometimes though I just buy inexpensive HSS bits and just switch them out when they start to get dull (especially for unique or low usage sizes).
For some materials I am a fan of bits that have parabolic spiral flutes, sometimes called Chip-Clearing bits. (The ones made for drilling Stainless Steel usually have an additional coating). Chip removal using parabolic flutes really helps prevent the risk of heat buildup caused by the flutes getting packed full while drilling. (Fisch and others even make parabolic bits that they label as "Pen Maker's Bits").
I am also a firm believer in specialized bits for drilling plastic and have acquired over time a comprehensive set that covers most pen drill sizes. The prices are not too bad until you get into the larger bit sizes. For example, a 7mm is just a little over $10. To me, the extra cost is worth it if it prevents me from blowing up a $10 Alumilite blank.