What do you do when your ears get cold and you're listening to a Walkman? Don't take off the earphones to put on a hat. Instead, replace the foam ear pads with Warm Ears, silver lame foam-lined earmuffs designed to fit any portable stereo headphone. You'll be chic, warm and still hear the music. Order from Warm Ears, R.D. 1, Box 441B, Barto, Pa. 19504. $7.95 (includes postage) ... Move over Clinique. Here's another brand of nonallergenic moisturizer, and it's locally produced. LaCrista products contain no fillers, alcohol, stabilizers, hormones, fragrances, mineral oil or other petroleum products. Formulated for skin sensitive to synthetic additives, the moisturizer comes in 2-ounce jars for $15, which includes tax, shipping and handling: LaCrista, Box 240, Davidsonville, Md. 21035 ... If you need extra-pretty table linens for a party, try Lovely Linens to Lend. Joan New (983-1910) and Gabriele Herer (493-5186) have an assortment of coordinated linens to rent, in paisley, plaids, solids and stripes. (If what you want is not there, they'll make it for you.) Rentals begin at $10 ... Ron Allan's interest in doors and doorknobs kept him just a few steps ahead of the wrecker's ball, but when his collection grew too large, he opened The Brass Knob. The new store, a showcase of architectural antiques, is located at 2309 18th St. NW. (332-3370). illustration: Story and song (By Annie Lunsford) photos 1&2: Flowers Notebooks (By Margaret Thomas)