There are long-reach endmills in various diameters — Garr makes some really nice ones in 1/8" diameter (which I guess is the wiki link you were thinking of), but as you note, they’re fragile.
===Long endmills===
- http://www.ebay.com/itm/10pcs-3-175x42mm-Carbide-CNC-Router-Bits-Single-Flute-Spiral-Cutters-End-Mills-/291866010066?hash=item43f491e1d2
- [GARR TOOL - Product Details Garr Tool Series 620MEDP#41030 1/8"x3x1"] — excellent quality, long narrow bit w/ a long cutting length which makes workholding and fixturing much easier, and making through cuts (w/ a suitable number of passes) on 1" material feasible.[Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable] [http://www.carbidedepot.com/detail.aspx?ID=73347 Carbide Depot]
- 3.175mm 2 Flute Spiral Bit Carbide End Mill Router 32mm CEL CNC Cutting Tool Sale - Banggood USA-arrival notice-arrival notice [Cutting 3/4" material with 1/8" Endmill - #9 by RichCournoyer]
- https://www.amazon.com/LMT-Onsrud-63-776-Uncoated-Diameter/dp/B001VXS2SW [Shapeoko3 2" depth HDPE - #4 by cod65]
- https://www.precisebits.com/products/carbidebits/deepreach125f2f.asp — intended for wax
- https://www.amazon.com/gp/product/B007BTQ502 [Shapeoko and Nomad Users Group (Unofficial) | Facebook]
- Amana [Let's cut 3" deep holes! - #2 by CNCInspiration]
** https://www.toolstoday.com/v-11872-46590.html
** https://www.toolstoday.com/v-12486-46490.html - Redline [Let's cut 3" deep holes! - #3 by DanStory]
** 1/4 (.2500) Diameter 3 Flute Single End Square, Carbide Endmill
** 1/4 (.2500) Diameter 3 Flute Single End Square, Carbide Endmill - 1/16
** https://bitsbits.com/index.php?main_page=product_info&cPath=138_1_84&products_id=919 [Longer Length of Cut - #17 by nystromd]
** https://www.amazon.com/uxcell-Carbide-Cutter-Acrylic-Hardwood/dp/B07KFTCH88
** https://www.ebay.com/itm/254524910002