Front racks that I recommend.

Winter Bicycles makes custom bicycles and custom racks. I requested a 6x10 rack to support my randonneur bag.
My bags fit this rack perfectly. The backstop on this rack is full sized, by request, and gives a rock solid interface.
​There is no bottom velcro, straps, or decaleur needed. 
Also, it is amazingly lightweight.
​https://winterbicycles.com/

Fitz Cyclez in Santa Rosa, CA offers custom complete bicycles, framesets, and racks. This 6 x 8 randonneur rack was built in stainless steel and fits my bags perfectly offering full support of the rando bag profile.
I strongly recommend working with Fitz Cyclez, an absolute pleasure and easy ordering process from an experienced and passionate cyclist and constructeur.
Stainless Steel, wet paint and powder coated tubular cro mo steel available.
http://www.fitzcyclez.com/

For off-the-shelf options, the Velo Orange Flat Pack Rack has a good shape  that fully supports a randonneur bag or porteur bag.
The rack is very adjustable and includes a decaleur and host of accoutrements to fine tune installation.
A little bit heavier than a custom rack but you will appreciate the amount of adjustability when moving this rack from bike to bike.
​So boom, ya done now.
https://velo-orange.com/collections/racks/products/flat-pack-randonneur-rack

Gallus Cycles in Colorado makes custom racks and decaleurs in any configuration. Racks are sold with custom frameset orders only. Contact the talented and nice guy Jeremy for more information: ​https://galluscycles.com/home.html