Where can I find burial matching nightgowns and robes?

Just adding my 2¢ .. seeing a lot of Golden Girls since mom has the remote and I think adding the word peignoir set to your search may help find something ... I saw some lovely things on Etsy.com. I've used Etsy for some adorable outfits for my granddaughter and most are true to description.
Good luck finding something lovely for mom !!!

Shadowline® Petals offer long and short robes and matching long and short gowns made of tricot nylon fabric with gathered yokes that feature floral embroidery & scalloped necklines. The neckline is high enough for my elderly mother to feel comfortable and "not naked" plus she loves the roses on the neckline. You can purchase these at National Wholesale Co. Inc. website: www.shopnational.com/brands/shadowline?cmpid=6080008&msclkid=5bdd701d8f3f11bad47a2ae787bfecd7&utm_source=bing&utm_medium=cpc&utm_campaign=YSM_Women's%20Apparel%20NEW&utm_term=%2Bshadowline%20%2Brobe&utm_content=shadowline

Vermont Country Store also has some very nice gown and robe sets.

They used to be offered at funeral homes along with caskets. May not be anymore. But you could call a few to see.
I googled “funeral burial gowns and robes”
Several sites came up.

HelpingMom, the Golden Girls have the advantage of studio fashion designers!

The Victoria magazine used to have ads for vintage clothing; I'll check my issues and see if I can find some names of companies.

There is a simple nice gown and matching robe available at Buck & Buck, it comes long or short and pink or blue.

thanks so much to all, hard to find, wonder how The Golden girls on tv have pretty classy nighties and matching robe sets?

Probably not the thing anymore

I found these sets on amazon. They look like they might be what you're looking for.

www.amazon.com/Vx-Intimate-Strappy-Nightgown-60563049/dp/B079YQ495F/ref=sr_1_77?ie=UTF8&qid=1525932842&sr=8-77&keywords=matching+nightgown+and+robe+sets

and

www.amazon.com/dp/B004X2G6B8/ref=sxbs_sxwds-stppvp_2?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=4775113870196211269&pd_rd_wg=G6wYN&pf_rd_r=A8HDSZH3KSFS7WFF4VGR&pf_rd_s=desktop-sx-bottom-slot&pf_rd_t=301&pd_rd_i=B004X2G6B8&pd_rd_w=doYOU&pf_rd_i=matching+nightgown+and+robe+sets&pd_rd_r=06695d5b-770e-4fca-bf75-20d63096d0f6&ie=UTF8&qid=1525933065&sr=2

and

www.amazon.com/dp/B079ZMX5Z9/ref=sxbs_sxwds-stppvp_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=4775113870196211269&pd_rd_wg=cepmP&pf_rd_r=ZBMH2S566EYWJ2XBNZ80&pf_rd_s=desktop-sx-bottom-slot&pf_rd_t=301&pd_rd_i=B079ZMX5Z9&pd_rd_w=FnVF6&pf_rd_i=matching+nightgown+and+robe+sets&pd_rd_r=92b9c0ad-120e-4165-ba08-095f653a57bc&ie=UTF8&qid=1525933184&sr=1

I would try Vermont Country Store. Or Victorian Trading. Both have nice long nightgown sets. I really like her idea! No bras or tight clothes. Perfect!